How does one start to forgive a betrayal?

I still don't know...My partner cheated on me 4 years ago and I am still not over it. He is my first partner, I think that is what it makes it more difficult for me. I guess what's meant to be will always find it's way. You need to live in the now. You can not control the future and you can not change the past. All you can do is enjoy the tme you have and try not to worry about what may or may not happen. It is so easy to write..alot harder to practice.I'm still having problems. My partner now works in a team full of females. It is hard to be happy, but I have to try! All you can do is enjoy what you have now.