I am exactly where you are now, and i know what you are going through, and the loss you feel everyday , for those that dont know, to have all this expectation about being a dad , first steps, first tooth , first words all taken away from you, its very tough, especially when a child is so young at the time, like in my case where they dont know you.
the time offered to me to be with my daughter has been severely limited due to her age , have to visit there, cant take her away for weekend etc , so every 2 weeks you basically feel like an absolute stranger in this little persons life for the few hours you allowed
i also "gave " up thinking that maybe its best that she doesnt know me, that she wont be confused etc, that has fallen through with the realization i dont want to live without my daughter , and will accept my limited role in whatever capacity , until such time as she is old enough and realizes what a father is , i pay without fail so she never goes without, and will be there for her when she needs me , and hope that the little time i get , that we can build a special relationship one day.
goodluck with your decision , and know that there are many individuals in your situation too, and its very difficult for an outsider to understand what it feels like to be cut out of someones life especially when they are so young and as a father you haven't fully realized the joys when they know who you are .
Hang in there and accept your relationship with ex is over and that your feelings will fade and you will get over it but the relationship with your daughter will be there for a lifetime ,and the loss of that relationship will haunt you for the rest of your life !