Sandman said it very well. I was in an long distance relationship that ended over the summer because she had cheated on me. I missed her when she wasn't here (granted...that was something that never happened, but for the purposes of this, that's okay), but I never put myself in the position that infidelity would even be a question. Honestly speaking and if it's not too much TMI, I gave up pornography in its entirety because I didn't wish to hurt her.
My point isn't to regale you with stories of my own accomplishments, but rather to say that fidelity and trust in these things are paramount, and without them, it is doomed to fail.

I did notice that alcohol is a trend in both these stories...does she have a problem with alcohol consumption? Her being under the influence doesn't make it okay, as that's still a responsibility issue, but that could be an underlying cause.
I am sorry you are going through this.

Personally, I think Sandman's impulse is correct, but I trust your judgement in the matter. You are in my prayers, and I wish you all the best.
Hugs,
Harley