Everyone was happy Suna was married to Osamu miya, and Osamu's twin brother, Atsumu miya was married to Sakusa Kiyoomi, Everything was fine, so why did Suna and Atsumu catch Sakusa and Osamu cheating?

Suna divorced Osamu and Atsumu divorce kiyoomi. Atsumu and Suna where lost and saw comfort in each other, they were 'friends' afterall and used each other to find happiness again

They grew closer than they already where and Suna, well started gaining feeling for Atsumu and even moved in together