dean found himself infactuated with you. he hated himself for it, truly, but he couldn't stop. 

he's not one to care about emotions or feelings, a one night stand is fine for him but everytime he thinks of you his heart squeezes and he feels stupidly soft. 

he hates it. but loves your affection. and you love his lewd comments.

so when you age regress to a younger age, like usual, he's happy to make time for you as your caregiver.