No, not "fall in love"; rather, engage in same-sex sexual behavior. It's long been known that many animals (among them, humans) engage in same-sex sexual behavior. In fact, more than 450 species have been documented. But, what has not yet been satisfactorily explained is how this benefits the animal in an evolutionary sense.
It is a given that the only traits that evolve are those that somehow benefit the animal. This benefit can come from providing a different sized beak for seeds (like the finches on the Galapagos Islands studied by Darwin), providing feathers for warmth (dinosaurs that evolved into birds) and camouflage (various examples). However, if an animal evolves a trait to engage in same-sex sexual behavior, what benefit does that provide? Scientists cannot yet answer this.
A new report reviews a large number of studies that have examined this behavior and discusses what kinds of benefits such behavior might provide. You can hear an NPR report about this research here.
You can read more about Darwin's groundbreaking research with finches here