I thought that at first. But after Jin and the father talk to Chiharu, I realised what his father is thinking. He's sending Kazuki away for so long and to asuch a different company (as stated many times) because he wants to completely severe what he sees as Kazuki's extreme dependency on Chiharu.
In his father's eyes, Kazuki is a mere puppet groomed for Chiharu to take charge of the company smoothly (he has some influence and now he even has the successor in the palm of his hand!). And that's what he's trying to change with this.
I don't think he knows they are involved romantically, but he must think that Kazuki is like a dog or something to Chiharu. He sees Kazuki's "blind" loyalty and faith in Chiharu without the romantic context and they seem like a puppet and a puppeteer. When is actually the other way around. Every action of Chiharu is for Kazuki's sake. And Kazuki knows damn well of Chiharu's shortcomings, limits and all that jazz. And yet he still is not afraid and that's what his father can't understand.
Anyway, that's just my opinion ╮(￣▽￣)╭
I think all of this has been a test for Kazuki and Chiharu. I mean there is no way his father believes that Kazuki and Chiharu relationship is still like a big brother/little brother or father/son. 5-10 years there's no way Kazuki needs that long to stay in America to learn. A year is really enough. I think Kazuki's father is doing this to push him harder and to show him that he will have to make sacrifices before and when he becomes president. Remember in Oboreru Kemono no Koibito when Kazuki traveled all the time with his father and Jin? His father knew Chiharu had Kazuki and it was a test for the both of them. For Chiharu to see how far he would go for Kazuki and for Kazuki to see if he could escape from Chiharu and put his foot down. Kazuki's gonna be his boss one day and if he just does everything Chiharu says and lets him do whatever he wants then Kazuki hasn't learned and he's not in charge. And now they have more test. Chiharu is gonna fight for him again and bring him home and Kazuki is gonna learn everything all in one year if they can do that then they pass. And Kazuki can finish the rest of his training at home and Chiharu can stay by his side forever. What do y'all think? (︶︿︶)