torturedpoet, first off, I'm so sorry about the loss of your mother. That must have been very hard, especially around the holidays!
I'm glad you've made the choice to separate (I remember your posts from last year, and this must have been a tough decision). Honestly, IHS the way you're describing is not a great long term solution. I've heard of people sharing a house after divorce if there's a basement apartment or something like that, where they each have their own spaces. Separate bedrooms isn't really enough, especially while you're trying to heal from his infidelity (your brain needs time and space away from him to form new patterns).
You mention not caring about him dating as long as he doesn't bring anyone home, but what if he does? Who says he'll follow your rules? What if he starts doing drugs again? How will you deal with that?
Before you make any decisions about finances, custody, roommates, etc., I would strongly urge you to speak with a few lawyers (many will do free consultations). My lawyer said IHS with legal financial separation is very difficult in practical/financial terms. Get some advice on what you can and cannot legally enforce in terms of your WS's behavior. They can probably also advise on whether he can share a place with someone else (usually this is okay, except in cases of abuse).
If you want to protect your money from his spending and you can't live separately, your best bet is to divorce him and then live like roommates. Another option to consider is a nesting arrangement. You could rent a room, and each of you spends alternating weeks there while the other lives with the kids. This is becoming increasingly popular, especially for parents of younger children who have a hard time going back and forth.