I just read this having been on the other side of the coin.
A gay friend of my housemate and mine became VERY into me. At first I thought it was just his forward nature and kinda played along teasingly as he knew I was straight. It started to freak me out when he came round and would follow me into my bedroom and tried to proposition me multiple times while we were alone after I hung out with them. I told him no and that it's not going to happen. I thought it was just being left there and he would take no as an answer and I left and he went back to hang out with my housemate.
The next time he was round I hung out with them again. My housemate, the chap in question and I all got high on E and GBL. When she (my housemate) passed out and I was in somewhat of a compromised state he relentlessly tried to fuck me. Kept trying to put his hands down my pants, or getting me to get naked with him, asked if he could give me head; tried to kiss me several times, I had to push his hand from under my top many times.
Eventually when I regained some mobility functions I left. Although the attention was flattering, it was frustrating that he wouldn't take no as an answer and wouldn't leave it even knowing that I was straight.
He was round a few weeks later and I decided that I wasn't going to interact with him because I didn't want to build up any hope in his mind; but he made every effort to bump into me whenever I was walking around the house. He wandered into the kitchen in his boxers when I was making dinner after I got home from work (not the best time for anyone to be pressuring me lol), kept trying to touch me up, asking me to fuck him. I left and locked myself away in my room.
Since then he has made several advancements over Facebook and tried to get me to invite him out. The sad thing is, he's a nice guy aside from the above and had he not been so relentless I probably would have hung out with him as a friend and he would have had me in his life to some degree. As much as he liked me, he couldn't respect how I felt... If I were gay, or a girl had been acting the same to me; alarm bells would ring, because the fundamental aspect of a relationship (in my mind) is mutual respect, and that wasn't offered, as it wouldn't be if you were to peruse the guy you like, knowing that he wont feel the same.
It's back-fired on him now; I told him that I'm not interested in the kindest ways plenty of times, but he clearly doesn't respect that boundary or my sexuality and so I've had to cut ties with him for both our sake.
If you really, and I mean REALLY love this guy, you need to be selfless and think about his happiness and respect that he is straight. I know he's not told you no, but the fact that he's straight and in a relationship with a girl should be enough indication that it's not happening. The more effort you put in and receive nothing back, the more broken you'll feel.
It's hard, but be happy that he's happy with someone he wants to be with. It hurts, but no matter what your sexuality, there's always going to be someone you can't have. It drives us fucking crazy and hurts like hell; but if you left school 18 months ago, you're still young, and have a much MUCH longer time than you've already experienced to find someone who will be interested in you and will return that love equally. That will be far more satisfying and rewarding than tricking someone into being with you; and to be 100% honest, if the aforementioned guy tried tricking me, then it definitely wouldn't go down well.
Obviously the above situation is different from your's in many ways; but none the less, a homosexual guy hounding a heterosexual guy when thinking only about their own desires doesn't always go down a storm, and I'd advise focusing your energy on you and finding other ways to make yourself happy.
Good luck
