A housemate of mine ended up with two women, and both had a child. All went well for quite some time. But, after that, he had to choose.
We had a couple of artists with multiple women here too. Funny, one of them was less famous than a few of his ladies. It worked well for all apparently. If it does, I cannot see a problem there.
I would get completely messed up, if I had to be in an intimate living situation with more than one partner. The social stuff would do me in completely.