Jansson had several male lovers, including the political philosopher Atos Wirtanen, who was the inspiration for the Moomin character Snufkin. However, she eventually “went over to the spook side” as she put it—a coded expression for homosexuality^{[18][19][20][21]} —and developed a secret love affair with the married theater director Vivica Bandler.^[22]

In 1956 Jansson met her lifelong partner, Tuulikki Pietilä – or “Tooti,” as she was known. In Helsinki they lived separately, in neighbouring blocks, visiting each other privately through an attic passageway. In the 1960s, they built a house on a tiny uninhabited island in the Gulf of Finland, 100 kilometres (62 mi) from Helsinki, where they would escape for the summer months.^[23] Jansson’s and Pietilä’s travels and summers spent together on the Klovharu island in Pellinki have been captured on several hours of film, shot by Pietilä. Several documentaries have been made of this footage, the latest being Haru, yksinäinen saari (Haru, the lonely island) (1998)^[24] and Tove ja Tooti Euroopassa (Tove and Tooti in Europe) (2004).^[25]

It is speculated that the character Too-ticky, a wise human who wears a red striped shirt and carries a briefcase, was inspired by Pietilä.^[22]