Have you had a chat with your son about how you want HIM to handle HIMSLEF yet? If you have'nt he's in a lot of stress on what you want him to do right now.
Also, you may want to offer him some guidance about further exposure.. he may tell his sister before you even do... siblings WILL do that...
Be a mom and give him a good long talk in a restaurant or soemthing.
This is the POINT of exposure :
a. It's theraputic for you b. It's respectful to your exposure group - they deserve to know c. It brings you closer to your kids d. It introduces hope for reconcilliation
It's a good thing, don't feel bad you spoke up... Don't feel bad anymore than a child speaks up to his family about being bullied at school
I assume you saw the Infidelty Intervention videos on youtube?
