Girls or guys, please help me sort this out. Does he have any feelings for me?

I would say it's possible that he does have feelings for you. Seeing you again after five years may have brought back all the feelings he remembered having and maybe he is realizing that he still cares about you. Maybe things with his gf aren't all that good and he is comparing his current relationship to what you two had. I would say the sudden stopping thing might be because his gf found out. Unless he himself had a revelation and realized he didn't care and he was just caught in the moment for awhile. I would try to reach him (if you care to keep in contact with him) and ask him what happened.