Toxic relationship in a nutshell.

There's an adorable manga called Yuzu-chan wa Harinezumi ga Sasatteru about a girl with a hedgehog attached to her body (most of the time her head) by its quills, who is trying to become her pet.

Completely unrelated to this, but I was reminded of it. Anyway, the lesson here is: people can get used to anything, for better or worse. Though she did go to the doctor once to complain about her head hurting all the time for some reason.