You come together for a bigger purpose, a spiritual ideal -- which, granted, isn't the most romantic thing two lovers can do together! You focus together willingly on ascending to greater spiritual heights. If your lover tends to be a cynical, pessimistic type (though they might call themselves realistic!), this relationship helps them to open up their soul a little bit and soften that hardened shell they've developed as a response to what can seem like an unstable world.
After all, their cynicism is just a defense mechanism they've developed as a response to various experiences that life has served up for them; it's not necessarily an accurate representation of the way the world really works. This relationship helps to open them back up to the intangible side of life, the mystical, ethereal, lyrical pleasures of love and human possibility. You help your lover start to believe in magic again, and they, in return, help you to stay grounded in reality. You might simply enrich each other's lives with your complementary perspectives, but you might also get into something more specific and directed in terms of spirituality -- going to church together or reading books about Zen Buddhism, for example. Even just gardening together helps to raise your sense of the mystery and magic of life while keeping your feet literally on the ground!