LOVE&SEX:
To get to the immediate point: Heero only truly "loves" one person: Relena, obviously. That said, his transfixion with Relena is well and truly deeply into personal goddess territory. Hell, just look at his cryocapsule in FT: he spends 30 years frozen inside what is basically an idyllic, goddess-like statue of Relena as his guardian angel. Relena represents almost every ideal he holds important: inner strength, courage, innocence without taint by ignorance, and most of all, inner and outward peace. She is at peace with herself, and more importantly is dedicated to the promotion of peace for others- hell the entire world where they come from. Peace is one thing that Heero has never been able to find, most of all within himself- however when they are alone together that is probably the rare occasion that he is able to find at least some part of himself that he doesn't totally despise- the part of him that is able to make her happy, for whatever reasons he still doesn't understand.
For him, sex is about showing her what an awkward, stunted child soldier like him can't figure out how to say- or at least what he finds pointless in words alone. Heero may be good with words in the oration sense (hell, he's a Gundam character, they're ALL good talkers in the cockpit), but when it comes down to it he's far better at speaking with his actions (another Gundam character trait). The first time he probably tried it just to see what it was like to be 'that close' with her, and continues it whenever she wants to (not that he has a hard time finding her 'sexy', but he's also sort of neurotic about it because he has trouble equating the 'innocence' he loves in her with the sexual attraction that he doesn't really understand).
Truly, I don't think Heero really even cares about sex- if anything, he's probably more into cuddling, because what he probably values about sex at all is the 'closeness' aspect of the act.
Yes, he is really THAT sappy.
As mentioned, he has difficulty separating 'Relena the ideal' from 'Relena the girl'. I believe that he truly fell in love with the ideal of Relena before he ever fell in love with her as a person. This should probably speak volumes of what kind of screwed up mixed messages he has for her, and probably brings about rather unfortunate results for her when it comes down to it. Relena the ideal is, as mentioned- the ability to bring peace, the inner strength and confidence that he himself lacks, the figure capable of moving an entire people with her strange power. However, Relena the girl is the Relena that loves him back, that chased him around the Earth Sphere at the beginning of the series and asked him not to die at the end of it- something he has difficulty coming to terms with when he has such a truly low opinion of himself. It is also the Relena he has whatever amount of sexual attraction to, and so most difficult about this is that, because of his self-deprecation complex, the idea of him 'dirtying' Relena the ideal in order to make Relena the girl happy creates a total war of wants within him that's left him quite and badly confused as to what he wants with her. Yes, he wants something with her, but he's too afraid of 'forcing' himself on her, and she'd be too demure to pursue him, that basically they just have a FESTIVAL OF UST and nothing ever happens- in-canon, anyway. And that's not even counting the difficulty he'd have of getting himself to settle down just in terms of he himself being unable to settle in one place for too long, or be the type of man- live the type of life she needs as a politician, and as someone who isn't as fucked up as he is.
In-canon I don't think he would ever get quite so close to her as he has in-game. Their in-game relationship is a result of him knowing that a) "Their work" for peace was no longer relevant on the Thor, at least not in the same manner or urgency as previously, and so he couldn't use that excuse as a way to force himself to distance himself from her; b) Relena would undoubtedly pursue him here without her work to attend to; and c) The ship is only as big as a single colony back home and a single colony is not big enough to keep Relena Darlian away from anything she wants. ;)
FAMILY:
Heero would say he doesn't really have any feelings towards family. In some ways he's lying, and in others, he's being perfectly truthful.
I believe Heero had a very detached, objective view of his mother and stepfather as a child- and now. His mother was Aoi, an Alliance spy who fell in love with Odin Lowe and pretty much begged to have his child before he turned coat and began working for the colonist rebels' side- and for whatever reason, perhaps to get the crazy off his back, he obliged. He left her once the deed was done and at some point after that she married another guy, Seis Clark, who was the lead engineer in the development of the ORIGINAL prototype Leo mobile suit. Heero never knows nor learns that Odin is his father, but he knows that his father ran out while his mother was pregnant with him, and he probably figures that he was also a spy of some sort- you don't get in that deep without your lover being in as deep as you are- and doesn't particularly care about him beyond that. Could be dead, for all he knows or cares.
His mother, he would say, was silly to have had him in the first place. She was a fool to have brought a child into the world and life she led- that of a spy, which even she realized, except she only did so shortly before her death. He would say it was a mistake he was ever born (indeed, he says when asked once 'I have been lost since the day I was born' (cheer up emo kid, etc). That isn't to say it goes into suicidal territory; yes, Heero obviously has some serious suicidal tendencies, but perhaps surprisingly, I don't think this enters into it at all. The other thing to realize is that Heero always acknowledges that his mother was "never his"- that is to say, he did not ever feel any love between them. When asked, she says she loves Seis 'as much as she loves him'. Considering it seems her heart still belonged to Odin, it was basically a backhanded was of saying 'not very much'.
His step-father, Seis, seemed to try hard to earn little Heero's love as his father, but Heero never really bought into it. As Heero said- 'you're mom's, not mine'- Heero seemed to have quite a fixation on the idea of 'ownership' as a child, saying that the only thing that was his was his broken Leo toy (something I'll explain in a moment), a trend I think continued until well into the time he was under Odin's care, when he moved on and instead of important came HIS ability to make decisions and to control HIS life- his life was his own to control, and thus the issues of ownership vanished. In any case, Seis had other issues- feeling under-appreciated and under-credited for his contributions to the early development of mobile suits, at one point shortly before his and Aoi's deaths he threw a fit, breaking Heero's Leo toy (that he'd given him), declaring him not his child, and throwing them out. It was after this that his mother said she loved him as much as Seis- the emptiness of the words more clear with context, hopefully. In any case, I think Heero perhaps felt great pity for Seis, especially retrospectively, perhaps far more than he ever felt for his mother. It's suggested in the novel that perhaps part of Heero's goal during Operation Meteor was to prove that the contributions Seis had made to mobile suits were not merely creating toys, as he ranted- that he should be proud of what he'd created. Food for thought, perhaps.
And then… there's Odin. His true father, though he doesn't know it- Odin is the closest Heero ever really got to feeling true 'family', I think. Unlike his mother and Seis, Odin gave Heero useful things- passed on skills, advice, and experiences- harsh ones that weren't sugar coated like the world his mother tried to give him. Odin also, to some extent, gave Heero the freedom to choose his own path, even encouraged it- in the end, Odin's last words became the ones that he would live the rest of his life by, most evidenced maybe in Heero's famous words, "Mission Accepted". He had the freedom to reject paths, if he so chose to. I think more than anyone, Heero respected Odin. If Heero did find out that Odin was truly his father, I don't think it would change a thing between them.
(PS: he did, and it didn't.. much, though Heero pities it a bit.)
In regards to... future prospects of family (which I don't think would happen in canon to be quite honest unless it was a mirror of how he had come to be born (Relena begging to bear his child) - and well, obviously didn't and prolly never will now), I don't think Relena has even registered to him as equating with 'family' due to the kind of "family" he grew up with, completely detached, the opposite of how he regards her. I think the idea of 'wife' would be very difficult for him, same with the idea of being a 'father'. He has never even remotely considered bearing children, but if he did, it would be very difficult for him to come to terms with the idea of family apart from what he was used to. I think while he'd be a loving and protective father, he'd be a really fucked up one to have, too- loving but constantly unsure and thus detached himself. It would take him time to come to terms with a new definition of family for himself.
POLITICS:
Where to even begin…
I don't think it's necessarily appropriate to call this section politics, but it'd be too complex to break it down into just 'beliefs', either. Politics imply, at least to Heero himself, everything he fought against- corruption, manipulation, everything OZ and the Alliance was. But, it's really just easier to call it politics, so politics it is.
--under construction..? 8D;--
RELIGION:
Heero is not religious whatsoever- he is pretty staunchly a man of scientific persuasion. However, just looking at his Gundam, it's clear that he has appropriated for himself symbols of certainly religious origin, and looking more deeply at him from a psychological standpoint, it becomes clear that he has a very pronounced martyr complex, even if he himself doesn't acknowledge belief in any higher figures.
Heero doesn't believe in "God" or any other unexplainable phenomena, but I think that he has knowingly borrowed religious symbols in order to outwardly express his own ideals- especially with regards to angels, and especially guardian angels. Innocence is an utmost ideal to him, and angels are the pinnacle representative of that ideal (see the section above regarding Relena, as that is basically the chief pillar of that ideal). That isn't to say that he believes these figures cease to hold religious values when he uses them; he's not as much a fool to think he lives in a cultural vacuum, but he doesn't mind what they "originally" stand for so much that he would be upset by their other meanings- besides, I don't think they would really clash with his own anyway. A belief is a belief, no matter what scripture is behind it.