All of my stories fit this prompt...
Every relationship I have right now, we got to through friendship, and every time there has been some crazy moment where friendship stopped being the label. Some moments are touching and teary, and some are a bit more flippant...
I thought A1 was gay. I had just come out of the poly closet to him, and my other close friends. We were cuddling on his bed, and suddenly he was confessing that he was in love with me. I cried and snuggled closer. Lying in his arms that night was one of the most sexual, powerful, beautiful moments of my life. (We were primaries for two years, and I think we're heading that way again.)
K and I were friends while I was closed relationship with other people. He visited me at my college one weekend, and we cuddled and talked one whole night on a couch in the common room, from bedtime until dawn. We both called it love after that... but didn't start dating for another year. (Primaries, getting legally married this fall.)
Found out I wanted R&J both when R discovered I liked being strangled. It shifted our dynamic pretty quickly. (Long-distance tertiaries.)
I was losing it-- senior year of college, high stress, dating K long-distance. Being sexually starved, I could handle on my own, but BDSM wasn't something I could do without anymore. I freaked out to A2, and suddenly her face was too close to mine. She offered to top me, and I felt so much safer. (Secondary these days, not my dom anymore-- she's my "girlfriend from the waist up".)
It was Valentine's Day, and Z was staying over at our apartment so his housemate could spend time with her fiance. He seemed lonely, so I offered to cuddle, then offered to make-out. We had so much fun we decided to do it again, and started dating for real a month later. (Totally primary now, and loving it!)
After literally four years of joke-flirting, I found myself sitting topless on M's lap, and realized through my tipsy-ness that he wasn't jokingly pushing me away. We had a wild make-out session that night, and it was spectacular. (Tertiary... still in shock!)
"I was thorough when I looked for you, and I feel justified lying in your arms." - Chasing Amy