It sounds like this woman really doesn't want much from a man, not really. On some level she's afraid of real intimacy. She jumps into sex because it's the easiest thing to do, for her. But she only likes what she can't have because that's "safe".

I agree with Bill, a therapist can help you learn to say no when you want to say no. Hopefully you'll build a much deeper relationship with someone who isn't afraid of a deeper emotional connection.