I'd just keep reminding myself it doesn't do any good to suffer consequences before something has happened. What if 20 years from now you wake up and you are still together and you realize you made yourself miserable for no good reason on a regular basis? If it ends, it ends, and things usually end for a good reason, even if it's not a fun experience.
What advice would you give him if you found out he was worrying about the same thing? Take that advice too. I imagine you might feel a bit insecure because you've been involved for awhile but the relationship bit is new, do you feel that if it was a lasting relationship it would've been official long ago? If that's the case, i'd recognize that becoming a "formal relationship" means you two made an intentional choice, and chose it instead of just falling into it, I tend to think that could make it a better bet for long term success.
I find I don't compare myself to other people if they are nice. If they are not nice to me, I compare. If I find myself comparing, I just say "Stop it, that's not helpful" Redirect your thoughts whenever you find it happening, and if you compare something negatively, follow it up with a positive compliment about each person too.
I find things less confusing when I read, and there are lots of great suggestions on the book and article sticky
Happiness will never come to those who fail to appreciate what they already have.