Is this how he went about getting you to marry him. "Hey baby, your boyfriends an ass. Dump the clown, move in with me and I'll show you how it's done!"
It just seems like you guys think it's OK to skip all the normal dating steps, because it would be a "poly" dynamic. It's not. If you really care for this women, be a friend! If you have her move into your home because she has no place else to go, do NOT date her. Once she is back on her feet, with a place of her own, then you can ASK her if she would like to date you. DO NOT approach her with your agenda of being one big happy poly family. Sorry, but it should take years before everyone moves in together.