When I was a teenager I did this too, it was part of my daily routine for years. I calculated sometime I likely have over 2000 individual scars.
It was the same feeling you describe, I enjoyed watching myself bleed, seeing it stream down. I'd even play with the blood sometimes, or put a few drops of it in my drink to give it that irony taste. Occasionally when I had a breakdown I'd overdo it quite badly, but usually it was just something I did because I liked it. I think self-hatred was a motivator, I felt like I needed to be punished.
Self-harm is an addictive behaviour, and it making you feel good is pretty normal from what I have heard from others who do or have done this.
Then one day, I just didn't feel like doing it. I was at my most unstable in a long time back then, when I finally realised what was making me so unstable, I realised what I needed to do to stabalise my mental state. And after that I just, stopped... I still yearn for it when I think about it, but the feelings are not strong enough to make me go back to doing it, but the cravings never seemed to go away, I will always like to see myself bleed and hurt, and I have accepted that.
I can't really tell you what your core problem is for it, but impulsive self-destructive behaviour is usually a sign of some form of instability, for me it was BPD, and I didn't know I had it back then.
Very rarely I still do it, usually when I have a breakdown, and it's entirely on impulse; but my desire isn't so strong now.
I know this isn't very helpful, but I think that you will eventually figure out what is causing you to engage in impulsive behaviours, and once you do, you probably will be able to stop a lot easier than it feels now.
Until you are mentally ready to stop, I'd recommend harm reduction over just trying for total abstinence; it is an addiction in my opinion, and should be managed as one.
Try to engage in it in a way that leaves the least permanent damage while still satisfying your urge, ideally as little as possible to satisfy it. Always sanitise your wounds and if they need stiches, get the stiches; that's very important for reducing long term skin damage. Don't cut deep enough that you could hit a nerve or artery, you can still bleed a lot without having to go that deep. Hitting a nerve is the worst case scenario and an artery requires emergency surgery to stop you from bleeding out.
Your scars might fade over time, or they might not. The smaller they are, the less likely they are to be immediately visible (which is why stitches are important), but for some people they just don't fade unfortunately. All of mine are just as visible 7 years later, so be prepared for that possibility as well.
If you can't help the impulse to cut deeper, lock your tools away in a place that will take you at least a few minutes to get to; this will give you time to calm down and think before doing something too rash. I don't know if it's totally possible to entirely remove the impulse here, but there are things you can do to at least mitigate the potential damage, such as intentionally getting blunter tools.
Good luck. I wish you the best.
And whether they fade or not, don't ever be ashamed of your scars; they'll be proof you got through it one day.
