I don't have children, op, and no one in my family has died by suicide. I know of at least 1 attempt however and have been suicidal myself on several occasions, so in your posts I recognise the torture you're feeling.
I also recognise your reaching out to find a way to cling on, because I've done the same. The fact that you're asking us is your rational mind knowing how devastating & irreversible the effect on your son will be and needing us to bring it home to you, because your pain is blocking you from feeling it.
But it does mean that as desperate as you feel right now, you have doubts and are looking for reasons to stay alive and that is a good sign.
Remember: suicide is a permanent solution to a temporary problem.
Sometimes, the 'temporary' bit feels like it's lasting for an eternity but it isn't. This will pass, and as hard as it for you to imagine right now, you will feel better and one day, not that far away, you will realise that you haven't felt suicidal for a while.
Then you will start to notice small improvements in your mental health, you'll notice them by the growing absence of your darkest thoughts before you notice the joy you start to feel once more.
Depression is incredibly cruel. It stops us from thinking properly, from believing in ourselves and our importance to others and hides hope from us. But hope is always there.
All you need to do is cling on by one fingernail for long enough and you will see it once more. I promise. ❤️
Take things an hour at a time, that's all you have to do. And be honest with your health visitor and GP, for your son's sake. Don't let him grow up knowing that he was your greatest joy but still not enough for you to stay with him.