Being a responsible adult is great. The pride from being on your own, accomplishing life goals, progressing in your career, moving up the income ladder to be able to own a home, a nice car and go on vacations. As for marriage you never know who is going to walk into your life. I wasn't looking for my wife when I found her, but married 26 years and going.
If you expect the first job you find you love and that you will stay at for 40 years, well you are going to be disappointed. But on the flip side if you think you are going to be in a job you hate, then you have are already decided to hate your job. You decide what job you will take and you decide if you are going to like it, love it, or hate it. If your first job isn't the best fit, then gain as much experience and skills as you can and when the time is right find another job. You are only stuck in a job you hate if you choose to stay and not look for something better. I've been working full-time for over 27 years. I've changed jobs 11 times. 5 where in the same field, 3 where in similar fields, and 3 were completely new. I left some for a better opportunity. Some I left because the company was going under. I was laid-off twice and yes I have left a job because I just absolutely hated it. But that is all fine. And fact is you may not always love your work, but you can love how you do your work. It is up to you.
Being an adult isn't terrible unless you make it that way. Most people see only the negative and never look at the positive. Will there be hard times? Sure, but that is how we grow. Life isn't all sunshine and rainbows. Nothing will hit you harder than life. But winning is all about taking the hits and moving forward. If you know what you are worth, then go out and get what you are worth be it in a job, a spouse, friends, hobbies, a home, or whatever. You decide your own happiness.