Yes, I relate to this. There are times where I enjoy things, but deep down I've always felt that unless something totally unexpected takes me first, I am going to commit suicide. It could be soon, or it could be years from now, but the feeling has lasted over a decade, through good times and bad.
Part of it, I think, is due to a desire of control over my own death. The thought that I'll choose when I go, and the circumstances surrounding it, bring me a bit of relief in this world I am incompatible with.
But I've also been wondering lately if part of it is to make it all worth it. If I suffer from ideations for years and years, then surely the inevitable conclusion for me is suicide? Because the alternative is - if someday I become content with life, somehow, and I live until my natural death, then that means those years of my life that were spent so fixated on my own despair and death amounted to nothing. If, hypothetically, I could learn to be content in the future, surely I could learn now, and so what am I doing, drowning like this? I know it's not a healthy way of thinking at all, but right now, the thought of recovery unsettles me.