His behavior shows lies, broken agreements, pushing you before you are ready... just a whole list of things that would be dealbreakers for me.
Before he admitted to the one night stand, our relationship was wonderful. He was nothing but trustworthy. He never mistreated me. I don't understand how this monster took over my BF. 9 years of wonderful and now this : (
I see that you are sad and I'm sorry you are going through this.
But your relationship is not wonderful TODAY. Worry about TODAY, not the past. The past is past. If your "todays" are stinky? That's what you are dealing in TODAY.
I think your conclusion of
I concluded I can't have a relationship like this, that maybe I should move on- citing my trust issues and mistreatment.
You cannot sustain a relationship like this -- it is dinging you in a lot of your OWN healths -- mental health, emotional health, spiritual health, etc. All this drama? You don't need it.
My only suggestion to you is to stop fighting to hang on to something that just won't fly.
You may want it to fly, and you may be willing and able. But HE is not willing and he is not able to put in the effort required. It sucks, but there it is. Over and over in your post -- he's not willing and able to make good on agreements.
So a break up seems in order here for YOUR best healths. That stinks. But a stink with an endpoint is better then endless never ending stink -- then you get to stop the stink and heal and feel better.
But staying here sounds like endless never ending stink.
You could start thinking about what YOU need to be healthy OUTSIDE of this relationship. Go with your conclusion and leave this stink so you can reach out toward healing and a better life.
Hang in there.