I have self-destructive tendancies. any suggestions on how to prevent them from taking over myself?

I wonder if ownership taking responsibility more for whatever it is that you are doing - Any action done often enough will start to become a habit so start to lessen the action try to find other behaviours that work wear an elastic band round your wrist and snap it once to make yourself stop the behaviour.

Find a way to be gently in control juts enough boundary to stop the unwanted behaviour and then keep reducing it - Sounds a bit mad but giving yourself a gold star for getting through a day without self harming can work keep a star calendar cash them in for a treat when you have a months worth

Fix your life. Only you can help yourself.