Actually, there was something Ou Xinhong did not make entirely clear. That was, Yang Yuqin had never loved Xia Liyou's father from the very start.
Her decision to marry him was made because she was hurt by the news of Ou Xinhong's wedding. Thus, she agreed to the arranged marriage. Xia Liyou's father was deeply infatuated with her, so they naturally ended up married.
Yang Yuqin was unhappy throughout her married life, which led to her inevitably following Ou Xinhong after a chance encounter.
She didn't even care whether he was married, whether he had once betrayed her, or if he would hurt her again. Nevertheless, she stayed by his side, resolute, like a moth drawn towards a flame.
Ou Xinhong did love her at that time, hence he never rejected her.
One could say, he was young and reckless at the time, arrogant, as someone from a noble family would be.
He did contemplate Yang Yuqin's forwardness, but he genuinely loved her then, so he didn't reject her.
