Yes, he's definitely pulled the manipulation card on you.

Was he abused as a child or witness to some sort of damaging event? In a lot of cases this is the case, but not in every case. Is he in treatment? He really should be. Basically he's having trouble coping with his own issues, most likely issues of his past.

Like with me, all my triggers are regarding some sort of relationship or people in general. I rarely cut otherwise. this means I have poor coping skills with people and I need to learn how to cope with others. I'm also a survivor of sexual abuse and other types of abuse that started in early childhood. To cope with any kind of conflict I often want to cut...but I do resist it.

You can't make him stop, but you can be there to support him whenever you need. It may not always prevent him from hurting himself, but at least it's letting him know that he has you to lean on. That's the best thing you can do for him. It's up to him to do the rest.