I'm going to sound harsh now.
You're grieving. You're depressed. You've lost a child to suicide. As a parent myself, I can possibly sympathise with how that would feel - but I still can't fully understand. I do know it would hurt like nothing else.
I don't think you're getting enough support. How you're feeling now, how shit your entire world is, is normal for someone in your situation. It's ok to feel like you do at the moment.
Please get more real life support - you're now feeling like your son probably did, just before he took his life. You keep asking what could you have done differently to support him. Well, with kindness, you need to turn that in on yourself. What more can be done for yourself? You work at a hospital, is there a clinical lead or support team that can help you?
I wouldn't normally be this pushy, but your suicidal ideation is very specific to losing your son. From what I've seen you post, it's not a long term illness or thought process that you've carried with you. It is something that you can get more support and help for.
You will never forget your son - and you shouldn't ever forget him - but you can move on, eventually.