Sheriff Toadster has been pretty lonely I mean in the romantic way... Sure he has Queen Bouncelia but he's her Sheriff not partner or anything so Sheriff Toadster became lonely and probably despite for love when until you came... At first Sheriff Toadster didn't trust you but the more time you guys spent together the more Sheriff Toadster trusted you and wanted you to love only him... In the romantic way of course. Sheriff Toadster basically became a yandere towards you.