If the sex is really good, go back with her for some fun but thats about it, keeping in mind that it wont last.
Dont marry this one though.
I agree. Short term might be ok, but long term it will likely not work.
Women tend to be much more forgiving about a guy who cheats for some reason. But when a woman cheats, she's damaged goods forever with the guy she betrayed. It can be overlooked for a while, but the mental images are always gnawing away in the guy's mind. A healthy level of trust is nearly impossible after that.
There are exceptions, I suppose, but they are not the norm. At least as I see it.