Fans began writing this period soon after Ruby's appearance in Season 3, before there was any canon relationship. The relationship was hinted at in canon from 4.01 Lazarus Rising, and confirmed in 4.09 I Know What You Did Last Summer, although canonically it was not exactly a romantic relationship, as Sera Gamble explained in this interview:
I referenced Monster's Ball right in the script. We were asking ourselves, "Where's the lowest place Sam can go in a state of despair?" That's why calling it a love scene strikes me as hilarious. It's kind of like self-mutilating and calling it getting dressed for the prom.