Everyone in some ways is getting what they want.
Everyone in some ways is not getting what they want.
Because we can dream.
Look at everything that has made you feel happy and fulfilled. Every life has some things like that. Now ask yourself which of it was something you dreamed and made happen and which of it was a surprise? I bet a lot of it was surprise and especially any of it involving people. Yet here you are, talking like this, so it apparently wasn't enough, yeah? Is it because you dreamed up more for those things than they had to give? What does this tell you about the usefulness of dreaming? I bet many of those good things also ended up facing difficulty as they touched the rest of your life. Such is the nature of anything, there are blessings and burdens in all things.
You can't be looking at what is past as something lost. Everything has its and context and then it is done. Even if you find the love of your life and get married, the nature of that commitment is going to turn into 50 different things over the course of your life. So getting attached to one idea of something that will be "what you need" is a folly. You will need many different things throughout your life and they will come in many different forms from many sources, many of which you have no way of predicting.
As for "missed" things, when something that was there isn't there anymore, either by leaving or by changing, look to how you were before you found that thing. You'll see yourself fresher, optimistic, explorative, inquisitive, experimental, active. Those are the things that found you something good that you cherished. If you aren't needed by anyone or anything in particular, that means you are free to return to that mode which discovers what gifts life has waiting. But they are out there waiting; you have to go involve yourself in the world to encounter them.
Take a step back and look at this world of 8 billion people. They are all just trying to survive, trying to connect, trying to find some enjoyment, trying to make a good offering. The spectrum of ability is very wide. What makes you better or worse than than any of them? We are all simple creatures that come and go and are eventually forgotten and even in great simplicity a life lived with attention is something made beautiful by the one subjectively receiving it. Getting caught up in dreams of what "could" or "ought" to be is a distraction from engaging and delighting in what is available to you.
So here is my main advice, which comes from much experience and education in psychology and neuroscience: You can't just think your way out of a mental problem. If the mind is the thing hurt/sick/weak then your mind is the thing that needs to rest and it is probably the way it is because it is overworked due to a lack of action in living. If life is fine but you are taking it as a problem to solve it's because you are not embracing how fine it is by living it. You can't direct a car that isn't rolling.