I would also advise calling the Samaritans. They will listen and are non-judgemental.
One thing about feeling in the pit of despair - it is really easy to feel that this is life forever now - that you will always feel like you do where you are now - but please believe me, whatever happens in your relationship, you will not. Life moves on. Things change. Where you are emotionally right now is a particularly shitty part of the journey, but it is not the destination.
Please reach out for real life support if you can. You are stronger than you think.
Your DS loves you and needs you. Your are not fucking up his life. You are just in a really low place at the moment, and things will gradually get better, and further down the line you will look back and wonder how you ever felt like this.
On a personal note, 2 years ago I was in the bottom of the pit for my own reasons - and I too thought I was fucking up DD's life. And do you know what? I didn't. Things improved, life changed, step by step I crawled out of the pit and my relationship with DD is so close and so joyful, I can't believe I ever thought that she'd be better off without me.
Sending you much love and 