If God isn't real where does love come from?
This one is complex, in all honesty we don’t know the exact causes of all emotions, we have several hypotheses as to why certain emotions evolved i.e. lust or love become useful tools in maintaining a mate and therefore propagating your genes. We also know that there are strong neurochemical reaction involved, such as the release of serotonin, oxytocin and testosterone in the brain leading to different sensations and physiological reactions which are then interpreted by the brain as emotions.
But I would like to counter the question with another question, what does the existence of one of many emotions have to do with the existence of a god? I would say that the question in itself is pointless, just because we didn't know the cause of certain emotions it doesn’t mean that the emotion was created by god, that’s known as a god of the gaps argument which is just a cop out.
Below is an image (from that wonderful Wikipedia) showing an extremely simplified chemical basis of love: