Most Helpful Guy
honestly? in my opinion you should break up, in that case she's just playing with your feelings, something like that is just unacceptable, maybe ask her what she means by a "happy ending" maybe she thinks it's something else, then it actually is, but if it is anything sexual, then definitely break up, it's better that way, she'll just hurt you even more if you give her another chance
Most Helpful Girl
If she intentionally went to get herself off with someone else, in my books that's cheating. But people define cheating differently, and she might not think it was cheating, because it was a paid service. You should express your feelings to her and tell her that it crosses the line of cheating for you (if that's what you think).