Although Lavender was known for being a bit boy crazy, she really didn't have that much experience with them. Her only real relationship had been Ronald and she didn't even like to think of it anymore. She wasn't sure what you were supposed to do in a situation like this.
Weeks? Lav had assumed it had been a one time thing, that they had been caught right away. "Do you think it would have been better if they had told you right away? If they hadn't hid it at all?" Lavender thought she would have, but she didn't know. Both might be equally awful.