The Evolutionary View
Every effect is determined by its cause. The apparent cause for our existence, knowing what we know from Mr. Darwin, is the process of natural selection. Natural selection transformed a cell of water and protein into the god-like transcended animal that thinks these thoughts and types these words.
And given that we went from that (basically zero) to this (basically infinity), every thing in our infinitude came as a result of the process — and that process being that those with the trait survived, and those without the trait did not.
Thus, is born the usefulness thesis of human nature, that we are what we are because it is useful to our survival that we be so.
And thus, the question of whether love is real, or an effect, or a whatever is the wrong question — we are robots, sure, but robots who love.
And why do we love?
Because it is useful to do so. Because without love, we are taken by the wolves, and die.