I'd be much more freaked out over the cutting thing. I've been around the block a few times. You are taking on too much with someone who is willing to self multilate. She probably cheated because she was drunk, alone and you guys aren't married. Cutting herself is a whole lot scarier.
Don't let her self mutilation stroke your ego. She did it because she has real troubles, probably not because you are so special. (Although I bet you are very special
)