What do I do about the girl I know will never be mine?

Alright, so I have a close friend and as long as I've known this girl I have been deeply infatuated with her. She's pretty, genuine, the whole deal. Problem is, she's had relationship with my best friend before and even though they're not together anymore they're still sort of the "Ross and Rachael" of our circle of friends. As in that they're sort of destined to be together and that it's universally agreed that they probably will be someday. I've always been this girl's "funny" friend, so I don't think I've ever been considered by her as a truly romantic option. Now, being brought up and let down by the possibility of us ever being together so many times I've completely given up on the notion of us ever having a romantic relationship. I've accepted that fact, but that doesn't mean I'm over her. Now, the problem lies in my future relationships. I won't ever be able to go out with anyone else because I would feel guilty about still having feelings(no matter how buried) for another person. So now I'm not sure what to do. Never be with anyone ever? And, don't tell me I'll get all the way over her someday, because I'm not that kind of person. Even if I was 40 and married to someone and hadn't seen this old love since my teenage years, I would still feel guilty about having an unresolved infatuation with another woman. What the hell am I supposed to do? Oh, and please no "Just tell her how you feel" answers, this is a complex situation that requires a complex solution.