I can't tell you how much of what you all are saying rings true for my life, too. My dd's birth father and I were also engaged and living together when I got pg with her. By the time I was 2.5 months pg, it became clear that it was not going to work (amazing how almost getting hit clears that right up for you!) For the duration of the pregnancy, and well into her first year, we tried to find a way to coparent. However, he just was not ready for the responsibility for himself, much less a baby, too. When she was 9 months old, the custody papers and child support got taken care of, and when she was 10 months old, we moved to DC area to be near my mom, who had cancer. We moved for a myriad of reasons. First, I needed to have myself and dd near my mom, and she needed us, too. It might have been a harder decision to make if my ex had any real track record of showing up to visit dd, but he didn't. I felt it was the right place in our (mine and dd's) lives to be at that time.
It was hard. Not just once we moved (it actually got easier then), but from mid-pregnancy on. It was also the best thing I could have done for us all, including my ex.
I struggled and juggled our way through the first 3 years of her life, working, going to school, and attachment parenting. From a few months before she was born, until nearly 4 years later, I had a roomate who was a single mom of two. She even moved to DC to live with us after I'd been here for about 6 months, because we had become a nuclear family when we weren't looking! She was a godsend to me, and vice versa. Sure, we had problems with each other, but they were outweighed during that time by the benefits.
I had many battles over child support with my ex. Also, I still clung to the idea that he wanted to be involved in her life, and tried to foist long-distance fatherhood on him. Even though he said that's what he wanted, his actions spoke volumes to the contrary, and that's what I eventually started to listen to.
In many ways, it feels that life has come full circle. Perhaps it would be more accurate to say it has spiraled upwards, because it's a lot better. 15 months ago, I married the love of my life (literally -- he was my first boyfriend when I was 14, then again at 16, 21, and finally at 24 through now). A few months before the wedding, when she was turning 3, dd started calling him dad, and now doesn't have any memory of him not being dad. He adopted her, and he is a fantastic father, if not completely AP.
My ex has a new fiance(e?), and they seem to be doing fine. She is older, with nearly grown kids who live with their father, so the yoke of responsibility does not weigh too heavily on him. This seems to be a much better situation for him, as well.
If it sounds like I'm all forgiveness-and-light about my ex, well, I've had nearly 5 years to get there. If you do end up becoming a single parent, you will get there eventually, too. Not that I don't think he's a schmuck, mind you; I wouldn't let him anywhere near her right now. But I've gotten over my hate and my rage, and even most of my anger. All that's left is pity, because he is missing out on such a great ride, and some forgiveness, because he truly wasn't able to handle it. Not that I excuse it, but where would holding a grudge get me?
That's my journey through single parenthood in a nutshell. It was the wisest thing I did for myself and especially for dd. One thing that sticks with me when I think about my relationship with the ex, and the relationship dd never had with him, is something that my late mother said about it. She was telling a coworker that I was pregnant, and the coworker said, "Oh, I didn't know they'd gotten married."
"No," said my mom, "that's the best thing about it -- she got rid of him!"
Feel free to email me if you need any advice, or just a shoulder to cry/lean on. I have, indeed, both been there and done that.
Good luck and Namaste