Questions: Dating

I am meeting with my boyfriend of a year who said we were on a "break" a month ago and ghosted me. During that time he hungout with this girl that during our relationship I told him he cannot talk to or we are done. They have done sexual things before and she sent me an extremely disrespectful text (disrespecting me and my boyfriend) 6 months ago. He wants to talk tomorrow (likely about getting back together). I really need either him to confess to me he saw her or I need to bring it up and clarify that if we do get back together he needs to cut her off permanently and he will not be going on "breaks" to talk to her every now and then if thats why he did this. His response to those needs is the deciding factor that is gonna make or break his chance of getting back together with me. The problem is this is his first relationship and he has a strong "fighting = broken relationship" thinking. And unfortunately I cannot bring up this topic without being mad and fighting about it. I was thinking of typing everything I want to say on a paper a bringing it with me and then being like "I don't know how to talk about this without fighting and I don't want to fight so please read this" and hand it to him. Would this be a good idea or weird/too much drama? Any other ideas? I just feel like if I bring it up by talking about it that it will lead to a negative conversation/fighting and I won't say the right things on the spot.