Making Partner Believe You Only Want Them

I need advice or tips; How did your partner believe you no longer wanted your baby’s father? I know for a fact I am completely done with my child’s father,I left him before I even gave birth. He’s a deadbeat. I left him for physical abuse reasons and because he was secretly dating men. I would literally die if I had to choose that over dating that man again. I’ve been with a woman whom I completely love and adore,I wish to marry her sooner rather than later I’m obsessed with this girl like completely obsessed with her my daughter lives her. I only want her all I think about is our future together with our daughter & our family after that. Fast forward to him getting 50/50 custody which now means split custody babygirl will have to see him eventually. How or when did your new partner finally realize that you absolutely don’t have feelings towards the sperm donor?