Read your OP, if I'm honest I see self harm as the lesser of two evils if the only other option was suicide. No, it's not socially acceptable, but sometimes we need to cope how we know, and sometimes, that is through self harming.
Someone I know who suffers with bipolar disorder, taught herself to tattoo. She now tattoos herself if she has that need to self harm because tattoos are for the most part, socially acceptable. I'm not saying you should do the same, but somehow she turned it into something more positive in a way, she's covered in some lovely artwork. I don't know if you can find an alternative, but try not to beat yourself up over this. I think so many go through ups and downs, periods of self harm and then nothing, sometimes for years. Then life becomes stressful, or something in your head just snaps and you go back to what you've always known.