Nothing else about your life changes. Real world, but either with this fictional character as a roommate or your favorite real person somehow becoming your friend.

Obviously ignoring partners, best friends, family and such here when defining this favorite person. Could be someone whose work you respect a lot, an important parasocial relationship in your life, just someone you really like, or anything similar.

Bonus round: the person you hate the most as your roommate or the character you hate the most as your enemy?