What is this guy's problem?

about 2 months ago, this guy i met (family friend) took me out to have some drinks with our co-workers who are his friends. we all work at the same place. i doing a trial internship there at the time. so it was cool to meet some new people, even though they were all guys. so one of the guys i thought was really cute, but he has a girlfriend. he was pretty nice when we hung out that night. i went home for 2 months after that trial internship, then came back after i decided to intern there for a few months. so i came back and now when i see this guy who i thought was cute (my friend's friend), he never says hi or smiles when i smile at him. he's actually kind of rude. like today i almost accidentally bumped into him and he gave me a bad look. he's not friendly at all. i mean maybe i should say hi but he's not giving off a very friendly vibe. he seems like a jerk, which is weird since he seemed nice that night.