I spoilt my son & I need to stop being his safety net
Your partner is right - but this is your child whom you love and are worried sick about.
I think he has no intention of taking his own life - he is being incredibly cruel and manipulative. if you offered to pay for his flights etc he would NOT go would use it as another stick to beat you with ("You want me dead"). If you don't agree to pay, then he will use THAT as a stick to beat you with ("You don't care how much I am suffering").
He is putting you in a position where you can't win, so that he can bully and manipulate you.
I know this sounds awful (and I don't know if I could do it), but you need - for BOTH your sakes) to put him out of your home and stop enabling his emotionally and financially self-destructive behaviour. Unless and until he has to stand on his own feet, he will never change.
He is a parasite - and he will leech of you(and emotionally abuse you) and when you are dead will do the same to your daughter. Cut him free now.
There is a chance that he will attempt suicide to guilt you into pandering to him - but he won't succeed (except by accident) because that isn't his intention. He doesn't want to end his life - he wants you to feel guilty so that he can continue avoiding his responsibilities as an adult by continuing to take from you.
Please don't let him.
As others have said, Dignitas won't just accept his view of his life - there are very strict regulations they must follow. Tell him you can't and won't facilitate his wishes, that you feel he would be better in another environment as he is obviously unhappy with you, and suggest he moves out of your home (Ill bet he won't).
Be prepared for histrionics - even some physically (self-) destructive behaviour, and behaviour aimed at hurting you specifically. But this is all you can do - for all of your sakes. As Pluck has said above - if he truly wants to end his life, he'll it - nothing you or anyone else can do or say will stop him - but that is NOT YOUR RESPONSIBILTY.
It is his. Suicide is a violent and aggressive act - but it takes courage. And I don't think your son has it.
My heart aches for you - you must feel sick with fright and despair, and be blaming yourself for all of this (it's a tendency that parents have), but he's an adult and it's no longer your responsibility. May I ask where his father is in all of this? Why is this on you alone?
Please get help yourself, too. You have tried to help him, but he doesn't want to change his attitude - all you can do now is change yours and let him get on with the course of life he has chosen. Stop enabling this self-pitying idleness - you must be dreadfully unhappy, too.
You deserve better - stop taking care of him, and look after yourself. Let your DP protect and support you for a change until you are strong enough to handle things. You are in dreadful position.