Special thanks to H for asking these questions...
Why I like these questions and put them as a post instead of just a comment is that I think many of us struggle with this or have thought about them, and if I reply as a comment then it's likely going to be missed out and maybe someone else may have the same feelings so I think it's good to share how I've handled these stuff...
As always, these are my own opinions and how I handled these situations based on my own experiences so... if it helps you that's good, else... just do whatever you feel is suitable.
I suppose there are 2 main questions here.
1) Joining friends and their activities
2) Living your own life and what if you regret it later
1) Joining friends and their activities
This is a pretty straight forward question and solution... from H's comment, I estimate him to be...