John lusts after Mona when he first spies her picture in the newspaper. He only takes the job of President of San Lorenzo to make her his wife. But unlike in a traditional romance story, Mona doesn't seem interested in the idea of love. At least, not love as in love, marriage, and children. Instead, she wants to share her love with everyone through Bokononism and boko-maru.
Although she and John become a sort of Adam and Eve after the ice-nine debacle, she opts out of the paradise-lost narrative by committing suicide. And that's pretty unromantic.