No, I don't think you're being selfish: You don't want what could feel like half a marriage, so you want him to make a more complete break with his wife, by completing a divorce he'll settle the issue with their house. It will be hard for him. But it's a responsibility he needs to take to honor his commitment to you. He needs to settle how to resolve the ownership of their house by talking with a divorce attorney. There's such a thing as "existential guilt" which is the normal suffering one has as a result of making a choice that dramatically affects the lives of other people. So he needs to accept that guilt. And you need to accept the guilt you might feel for insisting that he divorce his wife and settle his affairs in a way that the two of them and their daughters will need to accept also. I'm sure you've suffered a lot from the choice you made to marry a man who turned out to be abusive in relationship to you and your needs. And you probably needed to push past your own guilt about breaking up your marriage, if you were going to divorce him against his desire to keep you under his control. The power of love to push us forward on our journeys thru life carries with it the inevitability of suffering, which includes both hurt and guilt, along with loss and the fear of loss, and even frustrated ideal expectations (such as you may encounter when your present newfound bliss runs into the inevitable differences you will discover in your new relationship.
Choices as momentous as his are indeed difficult. but NOT to choose is WORSE for the maturation of you each individually and your relationship together. If he initiates the process of finding out how best to contract with his wife for the fate of their house, he find out that there are better ways to do it than he has realized; and his wife may suddenly get in gear and find herself another husband, or move back home with her possessive mother. The fear of loss by choosing is stifling the emotional energy that can propel you all into the next stage of your llives.