Why doesn't my ex boyfriend look me in the eye?

we stopped talking 6 months ago and then I run into him and we have to wait for the same bus so we start talking... and we get along great lol I make him laugh like crazy! lol he's so funny.. but I understand that he has a girlfriend and I respect him and am ok with it.. but when we were talking about our relationship (you know joking about the good times) lol he could barely look me in the eye... and then I ask him to look at me and I told him I still thought about him.. and when I looked at his eyes.. I could tell he was about to cry or (a large amount of emotion came over him) and then I looked away... and he got quiet and I changed the subject when we were together he barely looked at me when he knew that he was gonna see how sad I was or get sad himself.. he hides from his emotions often but I always tend to bring them out.. so why do you think he could barely look at me (slight glances as I spoke and when he did look at me he would get this huge smile on his face lol it was... Show More