"She knew she loved him when 'home' went from being a place to being a person." — E. Leventhal
Home is similar to one's lifestyle. Many therapists believe people actually fall in love with a lifestyle that the other person can provide.
That idea brings us back to shortcomings. What is a person missing that the other has? As an author, you won't go wrong if you write your romance to satisfy psychological longings.
Here are the underpinnings for two marine biologists to fall in love in One Night in Havana--