You don't say how old you are. I'm not sure you understand all the different things in life that can make a person happy or sad. As important as your job is, it's only one of the major factors in your life. Others include your family, your hobbies, your community, and your religion if you have one.
If your family life isn't happy, or isn't complete, or perhaps you don't even have a family, then it doesn't matter how much satisfaction you get from your job, your life won't feel complete. And vice versa. You may have the most wonderful wife and children on earth, but if your job sucks you'll feel like something is terribly wrong.
But back to the job. Some people like change. Some people like stability. You have to know which type you are before you can answer your question. I stayed in one job for 28 years. When I started out it was a pretty enjoyable job, but toward the end it wasn't so great. Still, I appreciated the stability, knowing that I didn't have to worry about being fired and having to look for a new job. Yet I finally left, and even thought I've had a lot of hard times and a lot of uncertainty, people tell me that I seem to be happier than I used to be because the work I do now is more meaningful.
Don't spend too much energy analyzing the lives of the other people you know. Try to understand yourself. Do you appreciate stability, or do you like the excitement of uncertainty? Do you like to stay with one thing and try to make it better, or do you prefer moving on to something else and hoping that it will start out better?
In addition to understanding how you feel about your career in general, you should also examine the rest of your life. The way you talk about your job, the words you use, the questions you ask... it makes me wonder whether other things are on your mind besides your job. Take a good look at your home life and decide whether something is happening there that is just as important as your job. If it is, then be sure to expend sufficient energy on it. Don't put all your energy into your job. It is not the only thing in your life.
I might as well close by telling you the same thing I tell everyone here: If you don't have a dog, get one. If you have one, spend more time with him. Dogs make life better. That's why they were the first non-human animal that we invited to share our lives.
Write back. We care.