When non-married parents live together as a family with their child(ren) only one parent should enter anything about the child on their tax return. The "sharing" of child related credits you may have heard about is only done between divorced or never-married parents who live apart and share custody.
So---one of you can file as Head of Household and claim the child and any related credits. The other parent files Single and enters nothing about the child on their return.
You can amend your return after it has been fully processed. Your GF's return has been blocked from e-filing this year. She will have to mail her return that claims the child. She can claim all of the child related credits. You cannot "split" them between you---except by sharing when your refunds arrive.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
