Native American baby's dad questions

He just left me and my other 2 kids he took on as his own unexpectedly over the weekend... I'm 27 weeks pregnant with his first child (which he begged me for).  I'm not denying him being the father because that's not questioned at all.  But do I have to give this baby his last name? He's Native American and I want her to have the benefits of his heritage but I feel like giving her his last name is giving him something he doesnt deserve after he up and left us for no reason.