Is this sweet, or just extremely stupid?!?!

So I have this friend who used to cut and has tried to commit suicide many times. He promised me that he wouldn't cut himself anymore, and if he wanted to kill himself he would talk to me. He NEVER breaks a promise. At least until now. A few weeks ago he made a deal with a friend who has a lot of problems right now that every time that she cut, he would. When he told me that I refused to talk to him for days! But then I just got sick of being mad at him... So I ended up talking to him and he apologized.

Today, (more like a few minutes ago) He told me that she cut, so because he made a promise to her, he had to cut, and how he said it was
"ok, please don't get mad at me or anything. i broke a promise, I'm so sorry. but i have this friend and she has a lot of problems and she cuts a lot. i told her if she cut again that i would cut once. and she did so i did. and i now she knows how i feel every time she cuts...
I'm sorry i broke a promise
but don't worry, ill never do it again and i have no urge to cut again
i promise. even though you probably don't trust me anymore..."

To be honest, I don't know that I can. I mean this is serious to me!
So I all I could really say was
"Thank you for telling me."
He then said
"its ok"
I then quickly responded with
"I'm gonna go...bye"

Which brings me to where I am now... I don't know weather to think it was sweet that he kept a promise to her by breaking one to me, or be extremely mad that this happened again... I mean I worry about him a lot. I used to check his arms for cuts anytime I would see him, I used to have to talk him out of suicide... Can I have someones opinion?