Marriage. Marriage is what brings us together. Or what tears us apart, depending on who you're asking. As a millennial whose number of married friends keeps increasing, it's hard not to think about the greatest commitment of all time (besides a life sentence). It's true that the marriage rate is declining in the United States, but maybe that's because people are actually making the choice to spend their lives with another person pretty damn seriously. That uptick of married friends? Well, none…