Welcome to beyond blue.
I cannot imagine what you have gone through in this last week and nothing I say will make it any better, but you are not alone. With the help of the psychologist, GP, friends, etc. I hope that you all get through this tough time in your life.
Yet there are some things that you can do - but mainly communication and education. If you have depression you (your son) might not notice it, or we are ashamed to speak out about our problems. I am not sure how much your son can open up to you. There are some things that I still have trouble talking to my wife about. And this is where the psychologist might be helpful. They are trained and expected to be non-judgemental and show empathy. For you, these are skills worth having. Just listening to your son talk about his troubles will mean a great deal to him. On the education front, and this is not necessarily just about suicide, but about being a support person. If you start here
there are some great resources.
Lastly a little story about me... One night last I was thinking about ending my life after the wife and kids has gone to bed. But I snapped out of it - I had sort of zoned out. I went back to the GP and then psychologist and was immediately given 1 week of leave from work. That turned into 5 weeks. My GP/psychologist wanted my wife to be with me 24/7 to make sure I did not do anything crazy. I had a alternative, and did not want to burden my wife in that way, so I would go elsewhere (College library) during the day time. Like your son, for the next while after that night I saw my psychologist weekly. I am still here.
There are other things to be considered like safety plans, removing access to needed items, but I am hopeful that you will have been told about this sort of stuff already.
And if things get really bad there is always 000.
If you have any questions, or want to chat, I am generally about.
Peace to you and your family,