tbh i headcanon sans being all right with anyone papyrus dates so long as

1. they treat him ok, and

2. sans can mooch off of the date

like mettaton is IDEAL because he is loaded. sans shows up in the middle of their date like “aw i wanted to hang out with bro today” and mettaton is like “i will give you 30 dollars if you leave right now” and sans is like “bye bro see you later.” he makes a horrible pun and pockets the cash