phoebe,
welcome to sober recovery forum. this site helped me through the most difficult time in my life and has been a lifeline. i hope we can help you.
we understand that you have given him numerous chances, we understand that you love him like crazy, we understand the shame that goes with it. we also understand that the power this stuff has over you CAN be eradicated.
right now, you need to focus on taking care of your children, and BEING THERE for them. can your son get some professional help? he really really needs it; these things don't just go away, even if the cutting does stop.
can you create a safe and peaceful home for the three of you? you will not experience that unless and until your husband has turned things around and has a good stretch of clean time under his belt.
even if he stops using right now this minute, that's just not long enough. with your teenage children, the stakes are too high.
i know you didn't ask for advice - i hope it's ok that i said what i did