Well...without giving too much away, she'll need to work on that self-loathing, and keep him safe from random hook-ups that might go terribly wrong. Not just on a sexual level, but just on a plain human level.

Shame is one of the main things that work for him, but so are pain and humiliation, and they can work on several levels. Nat will sadly have to go through a bit of mess herself figuring this out.

There's other things that can work, that he doesn't actually even like admitting to himself - but he will eventually, for Nat.

He's also not entirely insusceptible to new conditioning, but that's morally tricky, even for Nat.