Sweetheart, that is the illness speaking. If you died, you would leave a hole is his life which would never, ever be filled. It's true that he wouldn't have clear memories of you, but every birthday, every Christmas, ever major event in his life - graduating, getting married, his first job - he would be missing having his mother there to celebrate with him. Every little pain and problem during his life and he would wish he could turn to you for support.
I have been there darlin. I know how seductive that dark little voice can be, whispering in your ear that you'll never be good enough. I know what it's like to live surrounded by black smog no one else can see, to feel it pressing down on you so heavily it's hard to even lift your head in the morning.
Please, please seek help. And if you're already in treatment, please reach out to your doctor or therapist and tell them you're having a hard time. There is no shame in needing help. If you had cancer or meningitis you would seek medical help. If your little dark voice is telling you that no one cares, or that you're not worth the trouble, or that it won't work, or that you shouldn't waste their time because you're not as sick as some other people... it is lying to you. You are sharing your head with a stranger who hates you and is trying to trick you into giving up. Reach out and get him evicted.
If you're not already doing it, I can't recommend cognitive behavioural therapy enough. It teaches you to spot flaws in your thinking and stop them before they feed into your depression. Everyone reading this thread can clearly see that your thoughts are distorted by the illness - we all immediately thought 'Of course you are good enough! Of course your son would miss you!' But you can't see it through the smog.
Oh honey, please, please, don't give up. You can and will get better and I promise you that life without depression is a whole other world. Even the bad days are just bad days, and not the end of the world, and the good days are blissful. I am speaking from experience. I was sick for a long time. I cheated myself out of years of happiness by not getting help when I needed it, because I felt ashamed or unworthy. I'm better now, and every breath tastes sweet.
Reach out to the people around you. You might think they wouldn't miss you, but they would. Suicide shatters those left behind. You think they wouldn't want to help you? You think you'd be a burden to them? No. If you died, they would spend the rest of their lives asking themselves every day why you didn't reach out to them. There will be pain and grief and guilt and every night before they fall asleep they will ask themselves, 'Why wouldn't she let me help her? Why did she leave us?'
It pains me to read your post because I know that pain and it's so raw. Please take care of yourself. Get some sleep. Try to get outside and have a walk in the daylight, I know that might be hard right now. Try to get something nutritious in your belly. And if you need to, shut yourself away somewhere safe and ride out the waves where you can't hurt yourself. Call someone. Call the Samaritans if you can't bring yourself to discuss this with your loved ones.
Please update us and let us know you are still fighting on.