I just read your other post about his cheating, I am sorry you are going thru this. It honestly sounds like he was already pretty bad for your mental health, moving between wanting to break up and also talk about marriage and family. Unfortunately you aren’t ever going to get the answer to why he was swinging between these things while also cheating on you. Even if you did sit down and ask him and force him to answer, its not going to be the thing that makes everything ok, only time can do that.