I honestly think several people answered the OP to the best of their abilities, and their words were adequate--if not final.
A lot of this simply does come down to preference, with some prejudice thrown in, coupled with the fact that white gay men can afford to be more picky--as they are the majority in this 'community'.
There's not much rocket science or over-analyzing to be done on the matter.
I can say that from my experience (and I have dated and slept with a fair number of white men), for some white guys...black men are good enough to sleep with--but they wouldn't have a relationship with us. To some...we are only good enough to be their friends, while others won't even give us the time of day period.
That goes back to what I was saying about preference, prejudice, and being picky. Those categories are what you, OP, have been coming into contact with...you've probably ran into a lot of prejudiced gay white men. Yes, gay men can be bigots as well.
What many of us here are trying to tell you is that you can't let it get you down and define who you are. You have to have the confidence to know that even though there may be a lot of guys who won't give you the time of day because of your race, you still look good, and that doesn't make you less of a person. Hell, there are plenty of good looking men I see on a regular basis (black, white, asian, etc.) who wouldn't look at me twice--but that's alright--because I know I'm not everyone's speed. And yes, some of those men would not like me because I'm black. *shrugs* I'm not going to lose any sleep over it. Fuck 'em.
You need to find that self confidence, be proud of who you are, and stop grovelling over WHITE guys who are turning you down. I know from experience that there are plenty of them who practically worship black men. You just have to find the right ones...considering how...serious it seems to to you.
Having a preference for white guys is fine, but don't put yourself out there as if you have to live up to their standards or have their validation for your existence. That's pitiful and pathetic...and I'm sure you don't want to be associated with either of those terms.