I will go on the "old leather jacket" sensation.
When all you experience is one thing (pain, hatred, love, etc.) for too long, when we are put in situations that we aren't exposed to that one thing, it makes us uneasy and we feel out of our element. We don't know how to act. That one thing, no matter how detrimental to our well-being, gives us comfort, like the old leather jacket. It may be worn, it may not protect you against the elements, the spikes (if you like those type of jackets,) may dig into you to the point of bleeding, but after breaking it in and having it for so long, it just feels emotionally comfortable.
The problem is to abandon the old jacket, and try that new one, or make the best effort to put some distance between you and said old jacket.