How do I know if my boyfriend's friend likes me?

Me and my boyfriend have been together for a year and a half and recently we've been hanging out with one of his old "friends" from his AC/HVAC class.. They never hung out outside of school, so they've never been too close..

We've only hung out with him about 5-6 times. The first time we did, we went to his place for his birthday party. We were drinking all night, and he was smiling at me a bunch and laughing at just about everything I said, even though he was with this young girl (who wasn't good looking in the slightest) and I was with my guy. At one point during the night me and my guy started kissing, and I kept seeing him look over, when he finally said, "Alright, love birds..", which broke us up and he walked up.. Later he almost got in this fight with his neighbors which drew a lot of the guys at the party's attention, and after a cop pulled up and everyone was on there way inside, I was talking about how annoying it was, and he kept telling me sorry.. I'm having trouble remembering the rest of the night, but when I woke up the next morning, I wanted to talk to him.. (I'm totally interested! - me and my boyfriend are doing horribly, and he's really f***ing smart..) But when I woke up, I didn't know where he was, so I walked out back to just get some fresh air, and he was out there. He offered me a cigarette and I sat down.. I don't remember all the things he did and said, but he sure as hell smiled a lot and tried to make a lot of eye contact - which I'm not too big on.. He also kept apologizing for his 'almost-fight' and telling me about how it reminded him of the 'old him' and how he's not like that.. He was bragging about fights and talking about ex girlfriends like crazy.. At one point, though, I put my head into my hands because my head was killing me and he was like , "awww.." I asked him why he said it, and he said he thought I was shaking or something... My boyfriend woke up and walked outside a little later, and let us in on what time it was, and we were both like, "REALLY?" - obviously both thinking that the time had flew..

He doesn't text or call me or anything, but he remembers a lot of what I say.. He knows my boyfriend lives with me, so that's probably why. He's treated my boyfriend differently after that morning, too. It almost seems like he's trying to make him look like an idiot..

Also, at my birthday party a couple days ago, he asked a question, and I heard it, and answered him, and he was like, "Wow, you were paying attention to what I was saying? That's really cool.."

But good lord, will someone please let me know what they think... I'm going CRAZY...
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And he's got this long hair, so that morning, I teased him and asked, "So, what's the hair routine?" And after answering, he asked, "Yeah, so, what's your hair routine? You're hair looked really good last night.."
How do I know if my boyfriend's friend likes me?
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