Don't read if you don't want big spoilers because I couldn't explain it without spoiling it.
Ok so it's a little confusing. He's not the yakuza bosses 'wife' or still sleeping with the yakuza boss. The current boss is an old man and he has a lover. The uke used to be dating the yakuza bosses son, I'm assuming after the sons wife died or left as there was never a mention of her. The yakuza bosses grandson sends one of his subordinates to seduce uke to find out some info and they fall in love (yakuza bosses grandson left the group and made his own rival group so he doesn't have contact with his grandad and he's a bit of a tsundere and just wants to know how his gramps is
Does the uke sleep around? Does it show that? And does the seme sleep around? Does it show?