I agree that we don't know the whole story around Colin, but I have another impression.
Colin was the guy that allowed Amy to kick him in the nuts
(sorry just the way she told that story was hilarious). Now I think that he genuinely liked her otherwise he wouldn't react this way. It also shows that just like with Ephram, in this case Colin was the first to realize that likes the other one (in the case Amy) and to do something about it. And most boys would be pissed if some girl kicks them there btw.
The second thing I will always remember is this story about the trip where Amy missed the bus and Colin waited with her. Say what you want, but that was super sweet - the way he decided to stay besides her, to protect her and be sure that she will be all right. I don't think that jerk or jackass would do this. I see some responsible/sensitive guy like Ephram doing this.
Lastly we know that Amy and Colin didn't have sex. Now Colin was 2 years older than Amy (and he was Bright's age) and unlike his best friend he obviously didn't have the urge to have sex no matter what. He obviously respected Amy. Yes that might be the reason why he wanted to break up, but at least he was planning to not cheat on her and be honest with her. Just to mention something here - the fact that he didn't tell her doesn't make him bad guy in my eyes. Colin and Amy have been childhood friends just like Bright/Colin. Obviously he respected her enough and wanted to be sure that he wants to break up and obviously he waited for the right moment which is well very honorable. So this makes him actually good guy for me. Far more jackass move is to break up with her when she tells him that she loves him. At least for me it would be.
Jerry I saw this Bright's comment not like you saw it. Bright's bark was more dangerous than his bite. Bright wanted to intimidate Ephram and thought that by bringing you know his best friend (who had been always for him and who is in coma because of him) Ephram would back off. For me that was more like Bright desperately wanting his friend to be awake, fine and with him to be with Amy.