I wish just saying "Get Over It" would make things better for you. Obviously you can't help how you feel and that it's not that simple. Your ex and her trainer aren't going to last. It's only a matter of time before that ticking time bomb goes off and she'll be back at your feet talking about how it was a mistake, put on her sweet act and to give her another chance. You can SEE this coming. So I hope you are prepared for when it's going to happen. I think you got enough ammunition and hurt to really shake her up and kick her while she's down. It's up to you if you want to go that route, as she really deserves it. She needs some reality stapled to her forehead right now but I guess you can decide if you want it to be you, or just quietly and peacefully tell her that you do not want her anymore.
Not all girls are like that. It makes me appreciate everything I had before with my ex all the more. I'm sorry it had to happen like this.
I don't want to be accusatory here or kick you while you are down, but it's happened to you three times. There has to be something you are missing here and in your past relationships, as you are the common denominator in all of these mishaps. Did you just write off each relationship as saying "She's crazy, I did everything I could?" I just don't want to see it happen to you again. I know women your age are going to be more mature but still.
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.