Basically, I am full-blown beta, despite lurking the TRP for a few months.

This is what happened to me tonight. I went out drinking with 3 friends of mine (2 females, one male). One of the girls is in a relationship, the other is not (I've wanted to fuck her for years). The guy is a buddy from work (also BP). We first went out to a restaurant and ate way too much. Then went back to the girls (the girl I want to fuck) place for drinks. Things are going well. Later, both the girl and the guy leave. I am alone in the kitchen with the girl I have wanted to fuck for years. I tell her I want to go to the lake. She says she wants to watch a TV show. I try to hold frame and go to the lake despite her asking me to watch the TV show (probably a mistake). Interestingly, I forgot something, and return after a few minutes. She is texting a guy. She asks me what I think about this. I tell her "disgusting" for some reason. She says I would do the same. I then leave...

She wants to meet up again tomorrow. I tell her I can't because I am busy. She correctly questions wether I am actually busy. What should I do?

Please help me stop being Mr. Beta.

Feel free to ask for additional details.