Killing yourself is not the answer my lovely. I've been there and I know it's hard to look past but absolutely in no way is suicide the answer. You know this really.
You have NOT ruined your life, you're going through an understandably shitty time but it doesn't mean it's never going to pass. It will pass, and one day you will be happy again.
Let's break this down into smaller segments to try and tackle.
Your husband - does he add that much to your life? If you do everything by yourself anyway would you benefit from leaving, if at all possible? You don't agree with his discipline methods - is this child abuse? Your post reads like he is abusive and a "bad temper" does not excuse a shitty person. If you need support, I would suggest calling Women's Aid and going into more detail with them and they should be able to offer advice. Hopefully another poster will come by soon with some more detail on this, as unfortunately I can't.
Your family - you say your husband has caused a rift, is there any chance they would support you if you opened up to them? It sounds to me as though they see him for who he truly is, albeit I have only seen a snapshot of what the story is. Don't be too afraid to ask for help.
The debt - it is shit, but it's NOT the end of the world and death is not the answer. You might have made some bad choices leading to the debt, but today can be the start of making good choices. Starting by staying alive for your beautiful boys. I would start by making a list/organising the debt and sitting with a trusted friend/family member (if there's one available) and prioritising/coming up with a basic plan. Over time, you can pay it back, even if it takes years and years. That's okay. Today is the day you can look forward and start kicking down the walls that feel like they're closing in on you. You can do it.
Your boys - you need to protect them as well as yourself. And you can't do that if you're not here! I too have had thoughts that people would be better off without me, that I was useless, but the truth is that it's all in your head. They need you alive. You love them. You want to see them live a good life, and you absolutely CAN provide that. It may seem like you have mountains to move, but in reality it's squashing a few molehills - although I know all too well it can feel crushing on your dark days.
You have NOT ruined your life, you sound panicked and I completely understand, but think rationally, even though it is hard. You can do this, I'm here to check in on you and help where I can, and I'm sure others will be soon. Please, please seek real-life help and visit your GP ASAP or call Samaritans right this second. The number is 116 123 and they offer 24 hour support. The number is free to call.
It takes a village. I will be thinking of you, please stay here. Things will get better. 