Hi nowitmakes sense.
I understand how you feel. I started cutting as a teenager, and other than a few rough patches along the way managed to stop for years. But I've recently started again. I understand what you're saying about feeling low and disappointed afterwards (either in yourself or that you've let someone close to you down). I don't know how much help this will be, but here are a few suggestions my doctor gave me to try as an alternative to cutting.
His first suggestion was to use ice. It creates a sensation of pain but doesn't break the skin. His second suggestion was to ping elastic bands around your wrist. I personally find this one more useful than the ice. It give both the pain and a red mark after a while. It doesn't usually make the urge go away entirely but it sometimes lessens it to a more manageable level. His third option was to draw lines on your body, wherever you'd cut yourself, in red pen. This theoretically gives the illusion of a wound but again does no damage. There are also apps such as distrACT that you can download for free. It offers a range of ways to try to distract you until the urge to self harm passes. It might be worth a try?
I hope you find this helpful, I wish I could offer more.