It's sad because I think the right thing to do is walk away. I was a child in this situation and I did live with my not parent after the break-up. My actual parent is a mess, and this seemed like the better option at the time. In the end, I wish I stayed with my actual parent, as fucked up as it was. The false parent cared about me, but only when it was convenient for them. They actually were ok with me living with them, but it became apparent that they didn't truly want me the moment I arrived. I could just tell, they took me because they felt sorry for me. I don't think it was intentional, but rather that raising a kid is hard, and I could feel the resentment whenever it crept up. And it did often. I was her age. Just move on with your life and let them move on with theirs. Relationships ending is a fact of life. No need to drag it out.