I've fallen for a straight guy. And he's sending mixed signals. I'm a mess?

Hello! Phew, this is gonna be a little messy, but please bare with me. So, at the start of the new semester at college, I literally despised this one guy. I hated him, hated his guts, his ego, everything - you name it. But we were still kinda friends cause we had mutual friends in class and my lunch group and his lunch group would merge and stuff, so it was pretty hard to avoid him. As the term went by, the more we hung out, the more I started to see different sides of him. We'd end up hanging out together with just the two of us sometimes and I discovered so much about him through those moments. Yes, he does have a pretty big ego but I no longer seemed to be bothered by it? In fact, I would jokingly remind him that his head is getting too big. We got really comfortable with each other even though we're complete opposites. His confidence level is off the charts while I'm on the cowardly side. Fast forward a few months, we've done stuff like hug each other whenever we see each other in campus, me jokingly saying I love him and he's receiving all that well.. all the usual bromance thing, you know? I thought it was a bromance thing. But a few weeks ago when we hugged, he kissed me on the neck and I was taken aback. Then we held hands while walking down the streets (mind you, I'm in an asian country so people were staring 24/7) and he jokingly called me his 'boyfriend' at one point. He started doing all sorts of sweet stuff for me, he willingly protected me from the rain while he got soaked from head to toe. We've started flirting and made some sexual remarks towards each other as well. I was delusional the entire time and kept thinking this is all but a 'bromance' thing or a 'straight-boy' thing. I wouldn't know how they play those games, right? But here's the problem: I've fallen for him. I've fallen so hard for him, I didn't even knew I was falling for him. I was in constant denial throughout the entire semester, even though we were hugging and flirting I refused to admit that I was falling for the guy I despised before. But now I have. And I can't sleep every night, it's been weeks and I've been crying myself to sleep because I know I can't have him. Why? Sorry, I've left out an important info so far. He has a girlfriend.Which makes me so frustrated, so confused, cause what the hell is he doing with me then? From the start he knew that I was gay. And from the start I knew he has a girlfriend.I'm crying myself to sleep every night cause I don't want to be that person. I know I deserve someone better. But sometimes what I deserve isn't what I want? And I want him so badly, but I can't do that to him and his girlfriend. His girlfriend did nothing wrong, she'll be the biggest victim here. And it sucks cause my feelings for him are just growing stronger. I've been texting him everyday, We've been on call till like 2 in the morning, and he's been coming over to hang out and woah, bless me for keeping myself intact when it's just him and me in my room. Sigh. I need some help.TL;DR : Me, a very dumb gay college student, has fallen in love with a straight guy. And he has a girlfriend. BUT we've been touchy, we've been flirting, he's obviously showing a little interest in me?! Or is he just being nice?! I'm so confused cause, what the hell???