I'm depressed, why am I such a fool? Why won't I let go? I desperately need help!?

You sound like you are kind of obsessing over her. I think it would be ok to ask her to go to youth group with you, but don't ask the relationship question. It sounds like she may just like this other guy, and maybe you should not try to go out with her at this time. Just try to focus on other things and stop thinking about her. It is hard, but try to feel better and just pick up a good book or watch some funny movies, or hang out with your guy friends and get your mind off of her.