It still hurts after all this time...why?😢

Almost 2 years ago, my boyfriend went behind my back to get drunk with his crush from high school. (We are seniors in college.) it hurt me so much but I forgave him and moved on. But sometimes, the feelings from the night that I caught him and the pain that came with it hit me out of nowhere. I’m currently having sad thoughts about it now😢😢😢 and I have to keep quiet because if I told him how I feel after all this time, I know I will be called “crazy”😪