Them having known each other for a while, some flirting, but it becoming an official thing during one of those lulls? It was a very brief relationship in the scheme of things, but very intense, so there's a lot of lingering discomfort? Fujino's the type to want to take care of her partner and be taken care of in turn, plus there's a lot of loneliness for both of them so they were probably pretty domestic, too? Sleeping together most nights, that sort of thing.