How many times will I have to tell myself "I'm never going to do this again" for me to realize that self harm is not the right way to deal with pain?

That's a very hard thing to deal with, as self harm is addictive and often a primary coping strategy. But to help yourself recover, you have to establish new, healthy coping strategies, for example writing, holding ice etc, anything to distract yourself from urges. After a while, urges become less frequent and less intense, and recovery gets easier. But even then relapse is nothing to be ashamed of, it's what makes us human and is just another step to recovery.

When you are telling yourself that "I'm never going to do this again" you may only have to tell yourself this once, maybe a hundred times or your still telling yourself this now. Self harm isn't the best way to deal with your emotions, but until you figure out what other methods will benefit you then you will continue to say this to yourself

As many times as it takes for you to stop. If you do not think you will be able to please seek professional help

You never know. I've relapsed multiple times with really long periods of time in between self harming. You can never really tell unless you are stopping it for a reason other than just to stop it. For example, if someone you love makes you promise not to do it again then you may well stop forever because of it

There is no exact numerical answer to this because stopping self-harm is a long arduous process for many people (myself included). It's not something where you wake up one day and then just don't want to do it anymore, it's not something where just because you have nothing to harm with it's still not on your mind endlessly (speaking from my own experience so this may or may nto be your experience). It's something you have to take moment by moment and if that's day by day, hour by hour or even a few minutes at a time, whatever works for you goes. One huge help might be not seeing slip ups as end-all moments within recovery. They're not end all moments, they're moments that shape our path and they might be a step or two or three backwards, but they're not a finite "I need to start over and back at square one" sorta thing. You're doing what you can with what you have in the environment you're in and that's all anyone can ask of you. Treat yourself as kindly as possible too, that will help things improve as well. I'm here for you.