I'm so sorry for you and your daughter jmassie - I can't imagine the confusion you're going through. Was your marriage one of 'ups and downs" or were you completely unaware of any issues? Even then, if there were ups and downs, abandoning his daughter is abhorrent.
There's probably not much you can do except to start being proactive about the future stability of you and your daughter. Start with getting legal advice about child support and any other financial and legal issues which will arise. Also, find a support network or counsellor to help you and your daughter through this.
(((hugs))) to you
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.