I used to feel this way.
I'm 58. I was hospitalized this past January after thinking I had 'beaten' PTSD and depression years earlier. I even took myself off meds, lost 25 pounds, started walking daily--changes I have maintained.
Well, an unavoidable family tragedy knocked me into an episode that was truly frightening. Went to my GP, got the wrong meds, and ended up in hospital. It took me a LONG time after I was released to get past the feeling that I would never 'win'.
Now I look at it all differently. Some people have MS or cancer, I have this. I am living with this, not fighting it. It's part of who I am and I have to accept that, but I also know it isn't ALL that I am.
My spouse said, several months after I got out of the hospital, that he'd thought about it a lot and he realized there might be more, that I might not have been seeing my past very realistically. He is very supportive, but it shocked me to hear him say that. I had to admit he was probably right.
My pdoc had said from the start never to go off meds, that it was very serious and if I went off of them I might feel great temporarily but then something very, very bad WOULD happen... it would just be a matter of time. He was right, I was wrong.
Now I have a support system in place, meds, therapy, friends, work. I have to put my emotional health first and I do, and things go better that way.
I think I know what you are saying and why you feel the way you feel. But if you shift the way you look at it just a little, it's not really all that bad. It's not like all of life is terrible, it's just what it is. It's manageable. Not always easy, but manageable.
Hang in there.