So when do you throw in the towel?

I just happened to see her go into a male co-worker's hotel room with him about 5 minutes after she left me to “passout” (I was that drunk); so she lied about where she was going. .... I've read a self help book "Not Just Friends" and have tried for months to get her to at least read it so she might understand what I'm going through. She's refused and is sick of me bringing it up. It's starting to look like an impasse where I'll have to decide whether or not to throw in ...