i personally think that once you do this, you are giving him free reign to do the same, tit for tat, or give him an excuse to stop paying money into it, so be careful. But also remember that he isn’t really the person you thought he was, he may try and control things through the finances if he can’t get to you any other way.
If there is a lot in the joint account, you could take some out but send him a message to say you have transferred x amount of the joint account to safeguard paying the bills for x amount of months etc while everything gets sorted.
at some point you will have to have a conversation about practical matters anyway, especially regarding your 3 year old, but you can let the dust settle first, he owes you that at least.