My heart is with you. We have been going through exactly the same as you over the last year with our DS.
Firstly, check that your DS is still registered with CAMHs as ours had 'accidentally' been taken off the list. Secondly, if ANY suggestion or hint of suicide take him to A/E immediately, especially if they won't talk to anyone in person or over the phone.
Ours felt suicidal and feared himself and what he might do to himself but refused to talk over the phone to the support line at 05:00hrs in the morning. I rushed him to A/E as advised by the support line and on call GP and he was seen within 1/2 hr by a hospital psychiatrist and urgent support put in place immediately. We had waited 7 months for help prior to this.
I'm not writing this to tell you my story but in hope that the process we went through may help you.
Firstly we encouraged him to tell his best friends and talk to them about how he was feeling,to leave us their contact numbers, and ask them to call us at anytime if either DS couldn't or they were concerned.
I have been shocked by how many teenagers have been depressed and had suicidal thoughts, however thankfully for us all his friends have been very understanding and supportive towards him. He must always tell us where and when he is going and give us an approximate return time so we do not worry.(We have stressed that it is not because we are checking up on him, just concerned if we don't have this info)
Reapplication for CAMHs was inappropriate for us, as our DS was 18yrs old therefore too old, so I made fortnightly visits to the GP to start and monitor medication/mood. He was then referred for fortnightly support for 3 weeks from the GP practice mental health nurse.
She advised I wrote a summary of how our he was from birth until today, ie behaviour, habits, attitudes, learning capabilities etc.I have always had concerns (all very subtle signs)re behaviour, coping at school and learning accumen-DS struggled through school and left with no GCSE'S all of which were ignored by all.
She referred us to a psychologist who found my summary enlightening.
We have now been told, that our DS should have received support years ago as his depression is now deep rooted and has many underlying issues and that there are signs of undiagnosed autism and ADHD which are the likely causes for the depression and suicidal thoughts.
He has now been referred for numerous assessments in a variety of areas (and I have been referred for carers support) and his mood has lifted considerably just from the fact that, in his words
'Hallelujah, I knew something was wrong, at last someone is listening'.
I have cried nearly every day as I feel so helpless and lost, as I'm sure you do too. There seems very little support for any of us at this crossroads and what support there is is short and not necessarily with people that have gone through what we have, so I hope me writing this helps you in knowing that I know how you feel.
I'm not saying that your DS has the same issues as mine, what I am saying though is just let them know that you love them with all your heart, especially when it seems they are not listening to you, and no matter what, you will fight with every ounce of your breath to support them and try and find out what can be done to help.
My relationship with mine is so much stronger now, and although ,at times, he still struggles to explain how he is feeling, for the 1st time in a year he said 'Mum, I love you, thank you for helping me'. That's why we must fight through our own personal battles and focus on them.
It's worth life itself!
If you wish to chat further please don't hesitate in letting me know.