It has a Wikipedia article
here. It's all about how people fall in love. I especially liked the part about the physical effects of it. I don't know what it means, but when I visualize and mentally write out/storytell some of the love scenes in the stories I write, I get a surge of that feeling. I've ... um ... figured out how to trigger it semi-intentionally and become kind of ... yeah. I like it. It only lasts a second or two, but it's really cool to feel that way. And I meant "love scenes", not the sex scenes. The sex scenes are a completely different physical response. So now I have a word for that feeling I'm making myself feel: the sensation of limerence.
Physical attraction and
human bonding are worth checking out too, along with
attachment theory (SS Peter is securely attached; Gabriel is anxious-preoccupied, but he's graduating out of that into secure).