Advice on a boy's actions?

I apologize in advance if this is long.

Ok so I've known this boy for 2 years from work. He just celebrated one year with his girlfriend. We've always been like siblings, & people say we "bicker like a married couple" so we have a good relationship. And I definitely have feelings for him. But here's where I'm confused:

1) He drunk snapchatted me saying that I was cute and that if he was single, he would hook up with me.

2) He made a deal with me that if he's single by the end of summer, we'll hook up "for sure", in his words.

3) Another night, he soberly snapchatted me with no shirt on, and I playfully said "maybe you should put a shirt on, goober" and he said "maybe you should take yours off" (he wasn't drunk, so he knew what he was saying)

4) My friends have said that he complains about his girlfriend at work, about how controlling she is and stuff like that.

5) His girlfriend hates me, for what reason, I don't know.

6) He only flirts with me through snapchat, and always after 12am. It seems like it's because he doesn't want his girlfriend being able to see what he says since snapchats are deleted, but maybe that's just me.

I don't want to be 'that girl' that is the reason for someone's breakup, but it sounds to me like he's planning on being single, and that he might be interested in me? What do you guys think? Should I wait and see what happens? Or should I forget about it and move on?