I just had a 4 year relationship end with my fiance. I helped pay her way through school, was up at 4am helping her with her college schoolwork, went through a ton of hard problems cleanly over the years... Now she is out and working full time and migrated into acting as a fun hobby. While I work my ass off making 4 times her income to provide for a good life for the two of us and travelling for work, she turned out to be dating a cast member from a play of hers. Upon my return she wanted a break. After a few weeks of daily conversations to figure out the true story, I find out it wasn't a "break" but a death to our relationship. Looking back at our time together, I just feel used. Now I've told her I am glad we weren't married with kids and 5 years from now, divorced.
Look to the future and like it's been said, focus on your daughter and your future. Appreciate the good times and realize all those moments that justify this decision to move forward.
Unfortunately for me, I love my ex enough to worry about her future and her existence that I showed her how to open a checking account, pay rent, buy groceries, budget her money and move on with her life. I advise her on her dealings with work, with people and with her new man. And she still lives with me ("rent"goes to me and barely covers the food she eats) since she has nowhere else to go. Don't get trapped like me.
Good luck.