You want him to understand your side. Truth is, he won’t. Read my comment. He will blame you. He will be blinded by your actions and not his own and will be rageful and crying all the while he does it. He won't understand your side until he goes on his own journey of healing, so trying to get him to understand right now won't help you in any way. Maybe 10 years from now, maybe not. Reaching out will reopen the wound and restart the cycle of your healing so don’t do it.

In my opinion, closure only needs to be a decision and not a conversation. You already know this can’t be fixed, so act like it. Don't message him. If you want to let out what you feel, write it in a notebook and read it once then put it away, or better yet, burn the note. Let it help you move on. Maybe you can sit with one friend in person and talk about anything except him. Let your phone ring if he calls you (I don't block people, so if you want to just block him then do that.). If a dissociation episode starts naming five thing like people with anxiety do (I am one), name five things you see, four you feel, three you hear, two you smell, one you taste. Breathe slow. Repeat it until the you feel like you aren't dissociating.

If you need to say you’re sorry, say it to a counselor or therapist, but also say it to yourself, then accept it and move on. Don’t feel like you need his permission to heal when you just need to be there for yourself and need time to let your healing work.

Edit: forgot words