Polaris no Rakuin

Subaru Saeki is a widowed man who completely dotes on his young son, Sora. He is graceful and good-looking, but in reality, he’s a member of the yakuza, kept as the boss's male lover. At Sora’s nursery school, he meets a new teacher, Kousei, and it's love at first sight for Subaru. They begin to grow close, but Saeki gradually starts to feel that an icy flame is lurking in Kousei’s eyes...?

(Source: Cigarillo, translated)