Fairness is about being treated fair and having the same opportunities as others. It's natural to feel sad or envious at the joy of others. That's life.

Life is unfair in the sense that people's opportunities, abilities and experiences vary extremely wildly.

That is not fairness. It is un fairness.

Is being rewarded for nothing fair too?

You mean this in the sense that this person has not tried to cultivate a relationship, but it simultaneously can be read to mean being born into wealth, born into a stable household that fosters strong mental health and sense of self, born into a safe and nurturing environment.

Lots and lots of people do not have these things have have to work themselves raw, physically and mentally, to the point they do not have the time or energy to pursue a healthy relationship, not that they even know what one looks like.

You phrase all of this as if the other person just isnt trying hard enough, is not putting in enough effort, when you have no idea how much effort the poster or the happy couple put into anything.