Alright, read closely.
I know my situation wasn't as long as yours and I'm sure and very sorry that the longer you are in love with somebody, the harder it hits when it doesn't seem to work out.
I have been in love with my "straight" really good friend for about 2 years now, it was honestly a love at first sight thing, he is a grade below me in highschool and I never knew who he was until I saw him in the hall one day, I knew there was something special instantly, for about a year we never really talked at all, we became friends through a mutual friend and began to hang out quite often, all 3 of us. I even got to hang out with him alone quite a few times. Fast forward a few months, summer of 2011, we had been hanging out for about 7 months and and I my love for him just kept getting more and more intense.
At the beginning of this summer, I told him, and the mutual friend that I was gay, both of them pretty cool with it and we continued to hang out all summer just like we used to with no problems at all. Great! I think to myself, the guy I love is cool with me being gay, and he still hangs out with me, maybe I have a chance.
He had a girlfriend this whole time but I honestly say that didn't mean much and wasn't 100% sincere, so I just kind of ignored it. Near the end of the summer he got the idea that I liked him, we didn't talk for about a month, until school started back up, we ended up having a class together and started talking and hanging out again so everything was back to normal. About 2 months later, or about 1 month ago I basically started to have stress depression and anxiety because of the fact I had to hide how I felt for so long while spending all that time with him, it was so hard for me to be with him and not tell him how I felt, everything he did was so perfect and he was so perfect, I couldn't hold it in any longer.
So about a month ago or 3 weeks I decided I would tell him how I felt, I went about it real calm like and wasn't extremely blunt like randomly " HEY I LOVE YOU" I kept it calm and cool and told him slowly and smoothly. He seemed almost unresponsive the whole time I told him, it was pretty strange, one weird thing was he wouldn't make eye contact, also his hands were trembling like the fucking haiti earthquake (excuse the metaphor). his only response was "thanks for telling me." I asked if he had anything more to say, he said no, so I just told him it's best if we don't talk anymore, or at least for a long while, he started acting real sad, he said ok, then I left.
I wasn't sure what to take from that, he seemed so calm and unreactive, but the eye contact avoidance and the hand trembling really made me feel like my predictions were right, he may be gay and have feelings for me but isn't ready to accept it or tell himself he feels that way and really believe it.
Anyways I could go on and on about his and my feelings, but it's really too complicated to tell the whole story if you don't know him or I personally well.
I figured I would share this long tale just because it relates to you pretty much identically and it might help to know other people have experienced this many-a-time.
I thought I would be ok, and really I am doing a lot better than I was earlier, but I still love him so much, and I still see him in the halls every day, we have said hey when we pass to avoid awkwardness, but it still sucks, and I can't imagine trying to find somebody else to be with, that would help of course, but when you love somebody so much for a long time it really is near impossible to move on it seems. I still have the hope in my mind that he has feelings for me and just will accept it and maybe tell me when he's ready, I can't mope around waiting for that though, and neither should you. I know firsthand how badly this sucks, but you have to just be optimistic and try to either find somebody else, or find something to keep your mind off of him. Preaching to the choir there, I know that's pretty hard because I can't seem to do it myself.
I do recommend you stop drinking though, that really will not help you, I thought about doing it lots of times to cover up the pain, but in the end you're only making it worse by covering instead of coping.
I also recommend you try meditation, read about it online, master it, your breathing and focus will really help clear your mind and make your everyday life seem a lot less stressful and you will be able to divert your focus from your friend quite easily and stay happier a majority of the time.
Wow I just wrote a god damn novel, just thought that sharing my story since it was very recent and very similar to yours might help, also really, don't drink to mask the pain, just try to recover and focus your mind on the future and the good things in life, try meditation, art, music, dreaming, exercising, find something you like about the clouds each day, the trees or the grass.
Hope I could help

, sorry things didn't go your way, and remember, just cause he has a girlfriend, does NOT mean he is necessarily straight, and this may not be the end, but don't dwell on that.