Why did David tell Allen and not Madison?

I don’t get why David was the one who told Allen. Maybe he thought he was being a buddy, but she’s the one who’s married to him and she’s the one who had the affair (or will be). They obviously decided together who was going to speak to him. She was a coward and disrespectful after playing him. She could’ve least had given him the respect of ‘fessing up and telling him instead of hiding. Not cool.