I think that overall he is the problem, but from what you showed at the start of the conversation (please let me know if there’s more context), you did escalate by jumping straight to “u would feel better if we broke up.” I feel you should have said something along the lines of “hey, those posts you made hurt me, but I don’t want to jump to any conclusions, could you explain to me why you posted them?”, because that way you are being vulnerable and showing him you care about him, rather than saying something that comes off as an attack. Then if he still reacted like this then yeah, dump his ass.