It can be so hard not to get into those upsetting text exchanges. I've done it with my friend with the AGF, thinking all the while to myself, JUST STOP IT!
I've gotten better at simply not answering him if he texts something we are certain to argue about. It really helps (me, not his situation) to just Not. Answer.
So you slipped and engaged in the type of contact that is upsetting, it's okay, we all do. You just start again.