I just finished reading your sitch. You have P A T I E N C E down pat with all your H's antics. I have to commend you for putting up with an MLCer in the last three months and you have not strangled him yet. It really is a roller coaster ride for them. It is only by Grace of God that you have lasted this long. Hopefully, your H will hit bottom soon so he can move on to facing his issues. OW is just a bandaid...she will not be there for long. I don't know if I can do what you have done. I will cross that bridge when I get there.
Ask your H for his share of the bills in the house. If he makes more money than you, then prorate the cost and split it to that percentage. Doesn't matter if he likes it or not. Just tell him that this household is not a free board and lodging place. Everybody has to contribute.
One thing my H and I never fought about was money. We pooled our resources together and draw all expenses from the account. I am not a big spender and neither does he. When we split up, we also split up the cash on hand in the account. Now, I don't need to remind him to pay CS. He sends it a month early. But he is not home. Your H is. I don't know which is better. For them to be gone while they go through the process or be home.
If I remember HB's MLC recipe, it requires silence from the spouse while they go through the tunnel, into depression, and withdrawal and not to bother them at all if possible. So Cathy, just work on you and S4, be happy even if your H is being a butt about it some days, and some days he seemed to be decent.