Just want to see him happy?

I'm in love with my fiancé of 7 years. We had a fight this morning and I think it's officially over. My heart is broken. I don't feel like it can be mended. I have PTSD which is due to extensive childhood trauma. It causes me to self sabotage healthy relationships. A type of I'm going to run before I get hurt deal. He deserves so much more than what I believe I am capable of giving him. I feel as if I'm messing with his heart and I don't want to hurt him anymore, I wonder though is it possible to actually be happy for him? Do I truly mean it? I'm in love with him and he is in love with me. I want him to be happy but at the expense of my own broken heart, is it actually possible for me to be happy for him? Possibly seeing him with someone else later down the road knowing that I did this to myself. He doesn't want to let me go. I just can't keep hurting him. He's my best friend. He has been with me through my darkest of hours. We have a five year old daughter. So it's not like I can just up and forget about him and move on. How do it let him go knowing I am still so madly in love with him. It pains me so much. I'm trying to protect him from me. Will I ever be able to tell him "I'm happy for you" and actually mean it, knowing I made the best decision for both of us? I'm so broken and alone.