I'm married to my best friend and it's very hard for me to imagine what it's like for married people who don't feel that way about their partner. Sarah and I were friends well before anything romantic happened, and while it was a casual friendship at first, the relationship grew and deepened as we opened up over time, which eventually led to the sharing of "all our darkest secrets" (not so dark in hindsight). At some point – before I was even aware it had happened – we were in love. That's what made things so intense, and ultimately so scary: because it was anchored in deep friendship. At some point, it became an all-or-nothing situation. We broke up for a while in the early days, and while we did stay friends, whenever we were together and both single, well, there was boundary slippage. Then after getting back together for real, we hit a rough patch. And it resulted in this pretty blunt acknowledgement between us: that either we'd work this problem o...