A Partner's Betrayal

I'm a personal trainer, and yesterday was one of those rare times off-duty. I found out my partner was with someone else at my favorite park, on the same bench where we used to talk about our hopes for the future. He came back with a condom wrapper still in his pocket. Watching him leave with that evidence, I couldn't hold back; I felt like tearing apart the fabric of reality around me. How do you respond when someone else is your partner's chosen comfort in the moment you need them most?