I think he has concubines as something "mandatory" to a emperor but doesn't mean he has sex with them. That guy did say to Tei that Shuraka wasn't intimate with them
From what I've heard (so, take it with a grain of salt) about cultures where concubines and second wives are a thing, when the patriarch dies, his successor often "inherits" the concubines to make sure they are not pushed out and suddenly left on their own.
So this might be his father's harem.
That or it is more if a political thing, a way to forge alliances in exchange for the promise of an cushy life in the palace for the concubines.
I'm also not saying his intimate with them. I don't want to think that. I still trust Shuraka's loyalty. BUT! Don't you think he should've told Tei himself beforehand about him having concubines? In that way Tei wouldn't have to find out so suddenly and feel that he has no worth. I'm only mad bcz before he acted like he would never take any concubines, while he clearly has a ton. He should've told him. And he needs to clear things asap about that pink haired guy and him. Tei needs reassurance. Shuraka without realizing hurting his beloved. If you put yourself in Tei's place you'd understand his insecurities, his worries. It's totally valid. Just think about it, the person who always claims that you're the only one for them and they love above anything else suddenly has other partners too. How would you feel? Shuraka smelling like that pink dude make the situation even worse. They were already apart for 12 years. So it's hard for Tei to ask things directly given his personality.
For the first time I feeling so mad at Shuraka. In the past everytime Tei mentioned taking a woman as his consort he acted as if HE WOULD NEVER! While having a truckload of concubines behind the back. This must be a joke right?