[@Major Ursa] Unless Undyne's bi (And if she is she clearly has a heavy preference towards girls as heavily hinted at in her phone calls) and Papyrus was oblivious to not notice it (or it was early on knowing each other) I don't think he would've ever asked Undyne. Plus the two seem to have a purely platonic relationship.

My own headcanons aside, it's very plausible Pap has gotten many more dates once on the surface. He probably should add a few more standards or else there'll be more dates than days available, heheh.