I am so so sorry - you must be feeling so much internal pain to do what you did. After the way you're being treated though it's hardly surprising you self harmed, all that pent up anger & sadness has to come out in some way.
"Coping" with it though ...... you know the answer really don't you ? Unless your H was prepared to undergo counselling with you and admit that HE has a problem, the only way of dealing with this is to take him out of the equation - either by you leaving or by getting him to leave (the preferable option).
You say the children will be torn apart but if they already hear how their father verbally attacks their mother they are almost certainly already feeling very torn. They could grow up thinking that that is how women are supposed to be treated - like scum - and if they are boys, perpetuate that behaviour themselves, and if girls, end up choosing, and accepting the same sort of partner & treatment. Do you really want that for them ?
No-one will say take deep breaths next time. This isn't about judging you for self harming and telling you how to resist a razor blade, it's about you taking steps to ensure you never feel the need to do it again. While you remain with this man then it's very likely you will want, for a short while, to obliterate your inner pain through the distraction of self harming. When you are feeling that pain, you don't feel the emotional pain, but, quite obviously, self harming is only ever a near-momentary solution. The long term solution is to get away from him. He's disgusting, a disgrace ..... and what he's doing, isn't just about you, but is also mental abuse of his children by behaving in such a way in front of them.
You sound like a great mum and don't let him have you doubt that for a second. It's understandable to think you can't support the family on your own but you can and you will ...... 100s of 1000s of other women do. Admittedly, your life may change, but the loss of material things will be more than compensated for by the peace of mind and self confidence you and the children acquire instead.
Please, please look into getting away from this. Imagining him berating you in such a foul way is so upsetting ..... god knows how you must feel to be living it. What he's doing is abuse and I'd suggest you call Women's Aid: 08082000247 who can offer you all the support & advice you need to make that break. Yes, doing that is scary and may seem impossible, but it's not, and it must be better than enduring this for goodness knows how many more years. You will feel so much happier once you start to take back some of the control he has over you.