Envy combined with specific frame of mind. It says: "I work my ***** off and I'm alone because I have no time for people and that guy (a random friend for example) dates that girl and walks around as if he owns the world while he's doing very little compared to me".

I know, rationally, that it's about choices. And there is a price to be paid on both sides.

He's chasing around girls but the price is some average job he has.
I'm chasing career dreams and I get great results, proceeding towards something very special. The price is being alone.

I'm aware of it, rationally... doesn't change much though.