Unfortunately, when your partner goes through this sort of unfathomable fundamental change, you need to give him a short sharp reality check.
Show him how his future looks if he carries on like this whilst his fantasies are still a dream.
With such a young family you are very vulnerable at the moment and in an animalistic way he will see you as easy pickings because in his mind you are 'alone' ie unsupported by others whom he might respect more. (Probably not even consciously.)
Involve others such as your family, you need to effectively gang up on him and present a stronger, more united, front. You are now fighting for your family unit, so you need to open up to them. Don't let him see you as vulnerable, or lesser than him. In his new weird mindset you are a burden (sorry OP).
DH wont like it of course, and it might not work out in your favour but I think it is worth a try. You don't really have anything to lose as it will either bring things to a head quickly with a positive outcome, (more likely as although his head is wandering, his everyday reality is still enmeshed in the marriage,) or it will come to a head in a negative way. At least in getting there, there will be less time for torture and uncertainty and fighting that hurts you with his horrible messages etc.
If this brings him to his senses, don't let him off the hook easily. You need to regain his respect and he definitely needs to regain yours! Dump him unless he grovels convincingly and then some, and really really begs your forgiveness.
Otherwise you will set the path for more of the same disrespect, worse actually, further down the years, as he will think he has got away with it. It happened to me and I really should have got rid at the first sign of his shit!
Good luck, and I am sorry this has happened to you. Remember that if the family breaks up over this, it is NOT YOUR FAULT. On the contrary, you will have had a very lucky early escape. You are still young. Money, everything else will sort itself out, somehow, but you will have shown your children a very brave, very valuable lesson and can hold your head up high. x