If you make it far enough, you'll see how much it killed her when she realized her mistake cost her the only man she's ever loved. She was high on drugs/drunk, so it's easy to say she was susceptible to her lesser instincts and he likely took advantage of her in that state. If you can make it through that scene, you will be stronger for it, believe me. This game is not worth throwing away, in fact, the more it hurts, the more amazing the writing is. As long as you don't see her fucking the guy, and you're able to move past this, there is a chance for redemption for her and the MC. There is always hope for happiness and love, never forget that. You usually have to suffer first, unfortunately, though. That's the way I see it anyway.