I think the reason that I and other posters are appearing harsh is because we are asking you the follow-up question to your original one.
You said "AIBU to think he needs to grow up and get a job? And not rely on me as I'm working really hard and paying for everything and it's not fair."
We said no, very reasonable of you.
BUT the next question for you surely has to be "and what am I going to do if he doesn't?
If he will not take advice or help, are you prepared to support him for the rest of your life, or do you want an equal partnership, children that you can both financially and emotionally support, plan for the future together?
This is a very hard question, you have a lot of time and emotional energy invested in this relationship, and I am not surprised you are getting upset when people are basically saying to you either you have invested enough in him, now start investing in yourself and what you want, or, latterly, if his course is short, focussed and practical and he acknowledges and starts addressing any health issues then give it another go, but if not then walk away.
You can only make decisions for your self, you, I and the mumsnet collective can all say - he needs x,y and z but only he can decide to do those things.
You have to decide (and I do know it is tough after a long relationship) if your relationship is sustainable as it is, if he won't make the changes or taken the advice we (and you) have given him.