Math of happiness in love

Assume that on average people experience more negative feelings than positive ones in a life time.
When we love someone, we share the feelings of the other person. Thus, adding the feelings up, we will feel even more unhappiness when in love than when we are alone. But why do we still love others? Because in the above conclusion, we made an assumption that there is a 1 to 1 connection between every 2 person. However, if we present the argument that when the other person that we love is happy, the happiness that we originally felt will be more than if the other person wasn't around. That is, there is a more than 1 to 1 connection between people. However, that will only be true if the coefficient that is multiplied to happiness is more than or equals to the coefficient multiplied to unhappiness. But since we made a very powerful assumption at the start that people experience more negative feelings than positive ones in a life time, it doesn't matter if there is love. Therefore, love doesn't necessarily make us happier and the reason for why people love is not happiness.