What is normally referred to as "chemistry" in romantic relationships is not what we think of as laboratory chemistry - rather, it's the excitement that the couple experiences while interacting with each-other and being with each-other, which really isn't that different from a non-romantic friendship, except that in romance there is necessarily some amount of physical attraction as well.

Of course, people are biological entities, and biological systems are based off of chemical reactions, so ultimately everything we are and do involves chemistry at some level, but the "chemistry" of love isn't the same thing as the chemistry of atoms and molecules.