St Andrew's Insurance linked the January 2008 blaze in Margaret Street, Brighton – described in London's High Court as "the gay village" – to Tony Howe's tendency to "hissy fits". But Mr Howe, who has been with Jonathan Smyth, of Stirling, for close to seven years, said the fire, which killed the household's three cats, was an accident.
Ruling in favour of Mr Smyth, who is claiming around £300,000, deputy judge John Randall said the insurers had not satisfied him that the fire was started by Mr Howe.
It was more likely than not that it was started accidentally by a lit cigarette carelessly discarded or accidentally dislodged by Rebecca Alexander, who rented the basement room in the four-storey terrace where the fire began.
Ms Alexander, said the judge, was an "overly defensive" witness who made accusations against Mr Howe, which led to him being arrested, before he was bailed without charge and told he was not to be prosecuted.
She agreed she was a messy person and the state of her room, with clothing, tissues and a highly flammable bed cover, made it a serious fire hazard.
The judge said Mr Howe, who was 37 at the time, was not then employed but conscientiously undertook the housework, being fastidious and house-proud.
Sometimes, he had tantrums, or "hissy fits", which were in the nature of attention-seeking behaviour rather than being dangerous or destructive.
The judge said Mr Howe's essential account of matters and firm denial of arson had been calm and consistent throughout, and was convincing.
"I find there to be no cogent reasons for concluding that he deliberately started the fire."