Not sure I love her anymore

Try to be as nice as possible, but you are going to have to be up front with her. Don't tell any of your friends that know her about it though, even if you need someone to talk to, because if she thinks they knew before she did it will hurt even worse. Get it over and done with as soon as possible, don;t leave it hanging on cos sooner or later she will notice that you're not being the same around her as you used to, if she hasn't already. If you can't talk to her face to face try writing her a letter, she can re-read it and you can get your point across more clearly. Both you and her deserve to be with someone who you love better. Good luck