I agree it doesn't matter what others do. So let's leave that aside. I'll try and address your points about me honestly.

And thank you for taking the time to try and help, and for writing such posts.

Is my job rewarding? No. But no job is to me. My current job is as good as any job gets.
Health insurance - I'm in UK. So no, I don't get access to stuff like that. And even if I did, I wouldn't. Therapy not for me.
I'm not poor, but I believe being truly rich would sort out the boredom issue (I'm talking billionaire level). There's no way to achieve this, no.
I've done plenty of volunteering - it's boring and does nothing except make see more miserable people.

I don't think other people are unhappy to bring myself happiness, they're totally unconnected. I think most others are miserable because that's the evidence I have from them.

Yes, I've done it all. Not literally, obviously. But I've travelled a lot, done sport, done politcs, done art, watched hundreds of shows, etc etc. After a while it's all the same - I've read thousands of books, now they are all boring to me. I've tried lots of food, now it all basically is just food. I can't think of anything new I'm particularly interested in that I could afford to do.