White Out
The silly girl had left her diary on the bedside table. Didn't she realize he was a Slytherin?
As he heard her turn the shower on, he flicked open to a date some few weeks back. Something large had been obscured by some dried white substance. With a frown, Severus began to scratch away.
After a few minutes of dedicated scratching, he unearthed the entry.
My Wedding with Ron.
He quickly shut the diary and put it back in place as she came out of the shower. He grabbed her arm and pulled her back to bed.
Everyone makes mistakes.