It seems very likely to me that Garak and Julian would be the type to just sort of accidentally drift into a relationship without realizing it. Overtly flirting without realizing, they start giving each other gifts every time one of them goes on a mission, can’t make it to lunch today so how bout dinner at my place instead? Everyone else knows before they do sort of deal. Then one day someone offhandedly mentions “Julian’s boyfriend” and the convo moves on before he can reply and he’s like okay??? wtf???? Then that night him and Garak cuddling on the couch watching a movie as per usual and something just clicks and he’s like oh. OH.