Work can be stressful. This is true, no matter how old you are, where you are working, where you are in your career, what you do, etc.
Recognize that your coworkers are your coworkers, and your friends are your friends. And while there may be some overlap, the truth is, it's not complete, perfect overlap.
What that means is - cultivate your friendships outside of work, and complain to them
about what is happening at work. This is clearly a part of the problem; your boss feels that it is undermining the team. What I am suggesting is, save the sighs, etc. for after hours. It may be difficult at times, but do your best.