Both you and your H need to view this website. www.uptoparents.org This site is for divorcing and seperated parents. NEVER should a parent use a child against the other parent.
The issues you are facing with your H are ADULT issues. You both need to isolate the children, not include them.
From your own experience as a child, you know how difficult and how deep the scars can be.
The order of business is; Get yourself on track first. Second, take care of the kids and third, the marriage. Basically, if you aren't healthy, the rest will be difficult.
Also, educate yourself on affairs. There are many websites devoted to them. www.marriabebuilders.com www.break_free_from_the_affair.com save your marriage central all of which are unique in their own way. Learn ALL you can and move forward from there.