We made an agreement that he would at least stay until we've had 3 months of counseling (this starts next week)
This was before or after discovering the affair? You can try the counseling, but if it becomes fairly blatant that he's nurturing the relationship with OW (coming home late, going off with her,staying the night) then I personally wouldn't want him there...regardless of the 3 month deal.
In the end, it's not the years in your life that count. It's the life in your years. Abraham Lincoln
It is hard to fail, but it is worse never to have tried to succeed. Theodore Roosevelt