Hi Phil...
Maybe it depends on who you choose to tell, so please be careful.
Believe me there is nothing wrong with being single and not having a G.F.
I know it's painful and frustrating but you can manage without and just because you can't find her yet it doesn't mean you never will.
Can you try to find some way of distracting yourself from these intrusive thoughts or putting them in a less threatening place where they belong? Maybe a journal or notebook for example. That's what I do sometimes. Nobody else has to read it and you can say whatever you please. Hopefully, you might be able to see the thoughts for what they really are - THOUGHTS. Not potential harbingers of doom.
I would be very surprised if you were the first or last man who thought he was going mad or who was afraid of becoming Gay or dying. Me too mate...me too.
Like you, I have all these wonderfully irritating thoughts... and more, which I have to try and deal with on a daily basis. I've already had the experience of going into hospital on two occasions, so the fear of becoming seriously unwell again is something I can relate to.
I know it's difficult to find someone who you can trust with these fears. You just never know what kind of response you might get. Perhaps NMP is one small step in the right direction. You've already made a start with this Post.
Take Care and all the best