I'm sorry you're going through a tough time.
It might not be what you want to hear but ultimately, maybe it's for the best. Life shouldn't be one big long exhausting argument. Kids shouldn't be I'm an environment where their parents are on some rollecoaster of ups and downs.
If he leaves, life will be calmer. At least in the long run. For everyone.
Good on you for seeing a therapist and working things through. Its good that it's helping you. Hopefully it'll be a crutch through this difficult process.
I understand the impulse is to fight to keep the marriage. But I would see back and ask yourself if actually, life would be easier for you and especially the kids, if you split.
It sounds like he's spent amd cannot pour from an empty cup. That's not your fault. He let it get to this point too. But it is what it is. You'd be best to try to find a way to respect his decision.
That is, I'm assuming, if he really means it. You're sure this isn't a behaviour from him to get you to tow the line? Some people do pull that shit.
Either way, I think unfortunately, it's time to call the marriage a day. Or at the very least, try separating for a bit and seeing how you both feel.