Well the technical answer for this would be that, as is the case with everything, there are multiple parts of the brain involved. Dopamine, a neurotransmitter involved with emotions and various other functions, and serotonin, involved with mood and again various other functions, are very likely to be involved in a sensation of love. As far as the "pleasure" one gets out of being in love, this is controlled by endorphin release.
The hypothalamus is a part of the brain which controls such things as sexual behavior and is linked to emotion, and so it would be one part of the brain involved in feeling love. The amygdala is also very closely linked to fear, aggression, and other emotions. These two parts of the brain, combined with the thalamus, the nucleus accumbens (which controls the release of dopamine), and the hippocampus, make up a part of the brain known as the Limbic System, and this system in the brain is essentially the part that controls basic drives and emotions that a person has.
However, there are other parts of the brain that are involved in such things as your social life and behavior, such as the prefrontal cortex. So, to answer your question, the brain is an extremely complex organ. In almost everything that you do, there are many parts of the brain involved in making it happen. There is no one part of your brain that causes the sensations of being in love, especially since being in love spans such a broad spectrum of emotions, thoughts, behaviors and actions.
All of that being said, I also agree with the people that say it is spiritual. Though there are physical and mental consequences of being in love, i believe that these can only come in unison with a spirtual counterpart to them. Physical, mental, and spirtual behavior and actions all effect each other.