When Dr. Sato left them, it was only Ken, Yuki, and Grandpa Sato left in the living room. Ken was left with a lot of things in mind, what his father said makes sense and he indeed married Yuki out of sudden love and responsibility. The pressure that he had bonded with him adds up to it but every time they make love he felt something that he didn't feel when he was with Ethan.
"Ken…Your father and mother want you to be happy but they also don't want you to be the one who will cause the pain of the other. Your wife here…did you perhaps bond with him?" asked grandpa Sato. He had been wondering why would his good grandson betray his lover all of a sudden, the only conclusion he can think of was about the alpha-omega bond.
"Yes…I…" answered Ken
"I see…Did you want that bond to happen from the very start?"
"that…No, but I do now! I love Yuki so please do accept him"