Shen Yong didn't know that Sun Qinglian and Qiao Qing were cousins. He also didn't know that both the cousins were arch enemies of each other.
Shen Yong was coaxed by Sun Qinglian only because she knew that he was Qiao Qing's boyfriend. No matter what the reason, Sun Qinglian did not want Qiao Qing to be happy even for a minute. Thus she had seduced Shen Yong to snatch him from Qiao Qing.