Basically there yanderes that want you and you play as sans the one they want you.

Betty: "sansy~ kumu wants ypu to be with me.~"

Frisk: "sansyyyyyy.~"

Chara:"I'm the only normal one here but still sansy i want you.~"

Papyrus: "Stop doing this to my brother sans."

And i say again you play as sans.