Trust me, I get the whole "Why should I be the one to move out??" thing, but unless it's an ongoing affair or it's one spouse wanting to end the marriage and the other doesn't, why SHOULD she be the one to move out?
Puppy
In this case, because the alternate lodging is HER parents. If that is the only option, financially .... it really should be her. IMHO, but of course YMMV.
We've talked about possibly taking turns, alternately with her parents, while the other one of us is living in our house with our boys. At least until the real estate market turns around and we can sell it.
Of course, when she finds out I'm living with her parents, and wondering what the H I'm talking to them about, she'll probably go nuts and offer to move in with them herself, LOL.