Married people, why should I enjoy being single?

How should I enjoy being single? I have been single my whole life.

My closest friends are suddenly talking about marriage to some good people they have known for a long time, but for most were not courting for a long time. That's crazy!!

My friend actually gave me a lengthy speech about how he is going to miss his single life, and hanging out with friends because his girlfriend is very demanding. However, some of my friend's girlfriends are not very demanding.

I actually was not happy for him after seeing my friend after friend hook up, and I know that I should be happy, but since I have gone to a high demanding college to study chemistry without time for friends, unless it is like a break or sometimes a weekend or, actually I was pretty lonely at college, MY PERSONALITY HAS CHANGED!! I did not ask for that!!

We are talking "extroverted to introverted," so now my friend that was telling me to enjoy my single life, feels like I am not there for him because I am different. But, I did not ask to be different!!!

If it helps, I am 20 and a man.

Back to my original question, how do I have the most fun being single [no, nothing immoral or that will damage my body]?