I don’t really see how she was the “girl of a lifetime”. She cheated on you, she cheated on her long distance boyfriend with you, she wouldn’t communicate about an obvious problem (lack of sex) and then in the end she runs off with an even older man she barely knows? She sounds like a terrible girlfriend and person in general.

I think you are building her up in your head because she was young and beautiful. You’re chasing after a fantasy that doesn’t exist. If I was you I’d be happy that she is out of my life for good. As far as I can tell she brought more grief to your life than happiness. This is not the sign of a good relationship. They should make you a better person and you shouldn’t have to play games (like punishing her). You need to take off the blinders and see her for what she really is.

Do not punish people you love and care about, COMMUNICATE with them. You should have communicated to her early on that if she wants all of you she needs to drop the boyfriend. No one can read your mind, you have to tell them what you are thinking.

Hopefully you can at least learn something from this experience so your next relationship is more fulfilling and positive.