Thank you @Venage, @Mike, @Visforleo, and @Nick for your comments and encouragements. I'm currently opening up to old friends to better strengthen the friendships as I'm also trying to let go of a girl.
I met her a while ago, but she was dating someone else, so I thought nothing of it. I'm pretty sure she's single now, but what hurt was when I tried to get closer to her, another guy was flirting with her in front of me. I couldn't say anything directly (mostly because everything I thought to say sounded wrong, presumptuous, and hurtful). So I said nothing and started to write out my frustrations. It took time for me to realize my issue was that my low dating self-confidence and a fear of being alone. I over analyze situations, picture her as the "end-all, be-all", and invest a majority of brain power thinking about her, it's driving me crazy.
She came over one night for help on her homework, but oddly didn't bring any of her homework. She had limited time to turn in some assignments, but wanted to spend some of it with me. I want to believe that shows interest, but I think that she needs some time to be single, so I didn't want to rush things. I am talking with a couple of girls on OKC (one in Brazil. I'm in the US), so I have other options. Actually, one girl...the other removed her account.
What I am going to focus on is more mindfulness, especially when I'm near her. If I can detect a level of interest, then maybe I'll make a move, but if not, I will just let her go. That is one thing I need to learn, letting go. It's hurt too much by taking things serious and personal, and that might just be my hamartia.