Scenario #1:
So you & you're crush have been together for a while now and you end up going over to their house only to discover that they are now, well, a cat (who has the ability to talk) (or vise versa)

Scenario #2:
Pretty much the same as the first one but instead of being a cat you're crush is now just hand sized
(Or vise versa)

Scenario #3:
So one day you were at you're crush's house, and you heard some crashing coming from their room and you go to investigate, unaware that you're crush has now become a vampire
(Or vise versa)

Scenario #4: make something up!