Deltarune Toriel being a whore sucks, but it's god tier for Undertale Toriel, because it reveals that all of those headcanons of her being a lustful, repressed cougar are actually true, and means that if Frisk had stayed with her in the ruins long enough to grow into adulthood she 100% would have let him fuck her until they singlehandedly repopulate the ruins.
So there you go, play undertale, get to Toriel's house, save there and just leave that savefile be as you let them live the perfect ending.