Will caring a LOT help a friend who self-harms at all?!

I have a friend who has cut his arms and stomach very sporadically for perhaps 3-5 years. He's gone through so many girlfriends, yet he tells me that I'm the only person who's ever been able to make him not want to cut. I barely even did anything. When we were done with volleyball one day, we went back to his room and he took off his jacket and I saw very fresh scars running up and down his arms. There wasn't a square inch of skin that was devoid of any scarring. I was SO shocked and SO sad that he felt so much pain that he wanted to injure himself so grievously. I was very visibly shaken and on the verge of bawling, and he knew. I told him to please never hurt himself like that again, and that was all that was said that night about that.

He told me that what I did that night made him feel like someone care about him for the first time in his life, despite his long history of relationships. Even two years later, he told me that how much I cared helped him more than any of his girlfriends did (he's dated girls for years, they're not just flings).

Anyways, we were really close last January and at one point we were talking about his cutting and how he was moving away. He told me that without me, he feel like he might resort to cutting again, and that he would again feel suicidal. I was fairly composed for most of the conversation, but when I began to say "S------, please don't..hurt yourself. Please." I just lost it halfway through the sentence and was bawling by the time I finished it. He held me, and we talked about a lot more after that.

Anyways, I'm just wondering. Thinking about him harming himself breaks my heart. It hurts me SO much. Will his knowing how I feel about his self-mutilation at least help him a little?