What psychological phenomenon does the sentence "I am happy when you are happy" explain?

Explain that you are a more active person, will pay, and can consider problems from different angles.

Consider the other person first, because the happiness of others will make you happier.

Especially in front of love.

Do you know why many people are unhappy every day? Because they don't know how to make others happy.

So he is not happy himself, hehe.

Everyone's mood is changed by the changes of people and everything around him, hehe.