I think as a general rule, earth signs are drawn to air signs, air signs to water signs, water signs to fire signs, and fire signs to earth signs. Or put it more accurately, people are more drawn to those whose birthdays are two weeks to one month plus two weeks later, or four months plus two weeks to five months plus two weeks later than their own birthdays, or two months plus two weeks to three months plus two weeks earlier than their own birthdays.
Fire signs are more likely to settle down with fire signs or water signs. In fact, fire signs and water signs make very good matches, especially in politics.
Air signs are more likely to settle down with air signs or earth signs.