This.
It's pretty contrived though. I think realistically the two of them together would be glamorized as a power couple and it wouldn't diminish her/their popularity or success at all. I still think Ryuu and Kosuzu makes for the more compelling romance. tho
To be fair, Tei was in the middle of a major scandal that made her out to be a temptress and homewrecker. I doubt Takuma or the rest of the company leadership would let him maintain a relationship with her, and she wouldn't want to ruin his future.
But aside from that, I think there's a certain expectation for the wife/lover of a Zaibatsu leader. Kosuzu was expected to be at Takuma's beck and call, and I think he even took her with him to Manchuria. Tei couldn't do that for Ryuu, and even if he wouldn't expect her to, she doesn't think she could give him what he would need in a relationship.