If you are such a bad person, why did he come back, and keep coming back?
Sounds to me that he cannot accept the history (and reality) and that he will forever feel second best as you chose someone else over him. So he wants some kind of official statement that you effed up and it should have been him all along.
In that case, he should not be in a relationship if he isn't mature enough to deal with a persons history. And he definitely isn't mature enough.
Referring to your children like that is frankly, sickening.
Of course he is proposing marriage and wanting to push up the ante on the relationship - as soon as he has his feet under your table, that's when full control of you can commence, of you, and it sounds like your children too. So if you think it's scary now, imagine a time when there is no escape, or door to close with a sigh of relief.
He's lashing out at the moment because he doesn't have that control in his grasp - you are holding the cards and it's making him angry.
We've all been in relationships where perhaps the pace hasn't been where we thought it would - most people get to agreement by talking, communicating and sharing. Not shouting and sulking.
This is a toxic and twisted relationship, I cannot see how it will get any better if he keeps churning up a past he cannot forget, and letting it make him become so angry.