The number one cause of divorce is marrying before you hit all 3 requirements. You can't move onto the next step until you met all the requirements of the previous step:
1. The beginning. In the beginning you were drawn to each other somehow, looks, intellect, heart. The more and more you get to know them, the more and more deeply you fall in love.
2. The struggle. You fall in love but then you hit a road block and the flames are gone, you don't feel the same? If by the time the flames are gone and your relationship hasn't evolved into compassion, it's already time you both move on. Compassion is what happens after all the fights and all the struggles but somehow you two are still together, not because you never fight but because after every fight you guys make up, you become stronger. True love isn't a relationship that never fights, it's the one learns from every fight and only matures from it. If you fight all the time but don't learn anything, definitely time to move on.
3. Compassion. Compassion means the thought of leaving them doesn't make you feel right because you don't want to abandon them, you want to be there for them, you want to grow old with them. Only when you hit all three of these requirements should you even consider marriage.