Why do you say: People you love turn against each other?

That's not what the original sentence meant.

The original sentence is:

"If this relationship lasts forever, the person you love will betray you.

Who cares if you miss happiness? "

It means that if you live forever (meaning: a good reputation lasts forever), but the person you love turns against you, then you miss your own happiness. Who will really care about you in this case?

In other words, it is not worth turning against your lover for immortality; The only people who really care about you are the people you love and miss your lover. Others mention you, spread your good reputation, and may praise you, but they don't really care about you.

This sentence is the lyrics of the singer Alan's "Eternal Age", which is a song in the TV series "China". The next sentence of this sentence is:

"If you make a fool of yourself through the ages because of your obsession and confusion about love,

I don't regret being your disciple. "

It means that if you are laughed at because you are too persistent and confused, you don't regret trusting you and loving you for a lifetime.

Both of these sentences express the meaning that "you can be desperate for love".