That is certainly an interesting twist... I would say take it slow. For him to want to come back into the house certainly says something, right? At the same time, if he moves back in and the out and then in, what will that do to your D?
You should also know that DBing while living together is a whole new ballgame. I'm doing it right now and it's hard, really hard. The whole "go dark" thing is weird, since you see each other. You want to be nice and polite with each other, yet you want to maintain the DB "air of mystery". You want to keep your GAL going, but now have to take the roommate into consideration. It's just weird. It might be a little easier with a daughter who is so little because you don't necessarily have to "keep up appearances" as my W and I are trying to do with three older kids.
I'd still take it slow though. Set some ground rules and agreements.
Married 6 together 8 Me:38 W:31 second marriage for both SS12, SD10, S6 Bomb: 9/8/11 (day before our 5 yr ann) W moved out: 2/18/12 D final: 11/12/12 Share S 50/50. Spend as much time as I can with SS & SD