How did a new baby affect your struggling relationship?

We were very happy and we're trying for our baby daughter but as soon as she showed up my SO got cold feet and asked me to abort her. I refused and told him he could kick rocks. He ended up apologizing and we decided to work things out but things have not been the same since. We've gone from being so miserable and breaking up on even terms to becoming engaged and my getting a ring (that I wore for about 2 months before handing it back and breaking up). We are working on our relationship for probably the third time since we found out we were pregnant and I'm currently 34 weeks. She's due in 6 weeks and I just don't know what's going to happen. We're already fighting again but also living together, caring for his 4 year old son, and preparing for our daughter to come home shortly. From experience, how did the newborn affect a broken relationship? I keep my fingers crossed that our love for our daughter will bring us back together, seeing as how that's the reason we always decide to work on things.