I'm sorry you have to go through this, self harm is a horrible thing to deal with. Relapses usually occur when recovering from self harm, it's nothing to feel guilty about, so don't beat yourself up about it. If you explain to your friend why you cut yourself, I'm sure they'll understand, or at least sympathise and not get mad about it. If they have a negative reaction, it might just be instinctual, but they should eventually be calmer about it. If they continue to be angry, or upset, or act like it's about them, even after a while, that's a sign that they're toxic. But if you feel like you lied to your friend, or feel guilty for breaking the promise, remember that you tried your best, and you probably weren't fully in control of yourself when you relapsed, even if you think you were. Self harm is a hard thing to recover from, and recovery is a long process, some people relapse years after the stopped. I'm sure you'll eventually be able to fight that urge for good, and even two weeks without self harming is a lot, so don't feel bad. It'll take time and effort to recover, but I'm sure you will one day. Best wishes.