I feel you.
Relationship is not easy, and it does not always go to the direction that we had originally planned. However, hopefully, you have tried your best, and it is just time for you to move on.
From now on, you just have to take good care of your baby girl, you just have to try your best. It will not be easy for her to understand why you have to split with the mom. However, no matter what, you guys are till her dad and mom. You just have to try to present the best sides of you, and I think that should be enough.
Maybe it is not far for me to make these type of comments, becasue I don't have kid myself. However, I wish the best to you.
Just hang in there.