Long Story: Why is my friend acting like this? Should I give up on him?

Sounds to me like this guy has always had some sort of feelings for you, and maybe he was just too afraid to tell you. But now that you have a boyfriend who it sounds like you really like, he could feel that he will never get his chance with you. My advice, be straight up with him. Ask him if he has feelings for you, if he says no, then oh well. But i ure you, this isn't about the window.