(1) Traffic-stop test. If you're carpooling with a friend you root for more traffic because you enjoy spending time with them. Requires a sense of humor match. Other person should be fun. Respect for other persons way of thinking. A decent number of common interests. Otherwise a lot of what makes you ‘you’ will inevitably become a much smaller part of your life
(2) A feeling of home. Avoid discomfort because it will be multiplied by a million if you live together. Minimize secrets. Acceptance of flaws. Natural chemistry.
(3) Determination to be good at marriage. Communication. Study of divorcees say communication style top thing they'd change. Maintaining equality, one sides preference can't always prevail. Fighting well. 69% of fights are perpetual.