The only thing for those regets is to FORGIVE YOURSELF! If that happened it was because things meant to be that way,so it is better to let go, we in fact have little control about many things and most of all about our pasts.
I don´t hink it is a good thing to cling the happiness you think you have lost.
When we feel sad and lost we cling to whatever we find but in my personal opinion I would look forward instead of backwards. Rebuilt your life with whatever you´ve got
we all do that a lot. We start from scratch many times in this life.