What would you do?

My fiancé ex gf (we were together 1st broke up went different ways. But stayed in touch.) got pregnant and claimed it was his.  She had a healthy beautiful baby girl and he was a great dad!!! But soon after a while I told him to get a DNA test bc she looked NOTHING  like him. He didn't. So we stopped talking and communicating for a while. We saw each other one day and all the feelings came back. We got into our relationship I was trying to be a good step mom but I couldn't bc in my head I was like what if this isn't his kid. His gf figures out were together and showed him the DNA test.... He's not the father a WHIKE YEAR he took care of this baby did everything for them both and she knew... She's out the picture but now were actively TTC and he's all in  but then he keeps thinking of the little girl. Like birthday gifts parties outfits diapers .. Kinda makes me think will he be excited when we do concieve... Will I have to take a DNA test of the new baby? It's just not fair and I kinda just want to give up.... What should I do? Sorry for the little rant.