Personality revisions
Strangers and the average person don't get to see how Roy is with the people he's gathered around him. He encourages his public reputation for them presumably so that they'll underestimate his intelligence and skill as a soldier. With women he is charming and flirtatious, with men he is arrogant. He relaxes only around the few who have proven themselves to him through their actions and ideals.
He tends to place a lot of faith in his friends, and wants to protect them almost more than anything else. The only relationship we've actually seen grown from the beginning is the one he's built with Edward and Alphonse. At first they were just talented children who made a terrible mistake and he treated them as such. He kept their secret, but held it over them in order to get them to do what he wanted, and used them to further his own goals. As they kept on pushing forward and proving themselves Roy trusted them more and more until they too became friends he could rely on. He now treats them as equals more than tools, and has depended on them to do important things on more than one occasion. Including saving the country.
Allowing people to become that close to him also makes them his biggest weakness and trigger. He would go all out to protect them at almost any cost, and it's a tremendous hit when he loses them. He can't handle grief very well. When Hughes died Roy seemed to move on from the tragedy, not looking into the murder and acting like finding the truth didn't matter, but secretly he was harboring guilt at not being there, and anger at the killer. When he finally confronted Envy, who admitted to striking the blow, nothing mattered more in that moment than causing Envy pain and taking his revenge. This moment was the closest Roy had ever come to abandoning everything he'd built for himself, and it ultimately took Hawkeye threatening to shoot him and take her own life afterward to bring him back from the edge of his rage.
Roy doesn't seem to doubt very often, but he did surround himself with people just in case something like that happened (when he recruited Hawkeye to be his aide he specifically said that not only would she be watching his back but she would be able to shoot him in the back in case he ever went too far), so it's possible that he does not have as much faith in himself as he leads others to believe. He doesn't like the weaknesses he has, but he admits to them and plans accordingly just on the off chance that something happens.
He tends to place a lot of faith in his friends, and wants to protect them almost more than anything else. The only relationship we've actually seen grown from the beginning is the one he's built with Edward and Alphonse. At first they were just talented children who made a terrible mistake and he treated them as such. He kept their secret, but held it over them in order to get them to do what he wanted, and used them to further his own goals. As they kept on pushing forward and proving themselves Roy trusted them more and more until they too became friends he could rely on. He now treats them as equals more than tools, and has depended on them to do important things on more than one occasion. Including saving the country.
Allowing people to become that close to him also makes them his biggest weakness and trigger. He would go all out to protect them at almost any cost, and it's a tremendous hit when he loses them. He can't handle grief very well. When Hughes died Roy seemed to move on from the tragedy, not looking into the murder and acting like finding the truth didn't matter, but secretly he was harboring guilt at not being there, and anger at the killer. When he finally confronted Envy, who admitted to striking the blow, nothing mattered more in that moment than causing Envy pain and taking his revenge. This moment was the closest Roy had ever come to abandoning everything he'd built for himself, and it ultimately took Hawkeye threatening to shoot him and take her own life afterward to bring him back from the edge of his rage.
Roy doesn't seem to doubt very often, but he did surround himself with people just in case something like that happened (when he recruited Hawkeye to be his aide he specifically said that not only would she be watching his back but she would be able to shoot him in the back in case he ever went too far), so it's possible that he does not have as much faith in himself as he leads others to believe. He doesn't like the weaknesses he has, but he admits to them and plans accordingly just on the off chance that something happens.