She was playing house since she met Z. Correct me if I am wrong, but they weren’t committed to each other when she got accidentally pregnant. She took it as a sign and moved in together, started living together, paying bills and acting like a married couple. The truth is that Z never proposed. There wasn’t a relationship to begin with. A spark that resulted in a pregnancy is hardly grounds to think you should now become a family.
I don’t think either of them chose this life for themselves. Relationships should be built on a strong foundation. They didn’t have one to begin with. People who have strong foundations still find relationships difficult at times, but can weather those storms together more easily than two people who got together due to circumstances.
They should call it quits and concentrate on being good co parents.