Why is the onesh of znus with an arusah (Sekilah) more chamur than with a nessuah (checek)?
Rashi in Sanhedrin 50a D:H Al Korcach says that the reason an arus is more chamur than a nesua is because on one hand she is considered married to the husband since she is an arusa, but on the other hand she is still under her fathers wings. Therefore it is not only a terrible sin, but also an embarrassment and defiling her father’s family. I saw another idea in a sefer that znus of a nesua ruins the husband from continuing to live with his wife, and although it is a terrible sin, it is not as bad as an arusa which inhibits him from even getting married to her. Since the damage to the husband is worse, it is a bigger sin.