Why now, after 6 years? I'm guessing as he has young DCs, at least one of them was born within those 6 years? Why didn't you walk away then?
I don't believe that it's hard to leave and it's a relationship - it is a fantasy life, a double life. It brings deceit in all areas of your life, each time you kiss and hug your DCs, each time you get into bed next to your DH, each time you celebrate a birthday.
I was one of those pre-teens who found out about my DF's long term affair before my DM did. I carried on in pained silence as I didn't want to hurt my DM but it all came out in the end. Almost 30 years of hate, anger and disrespect towards my DF.
How do you know that your OM isn't / hasn't slept with others in that space of time? you are putting far more at risk than just sexual health. Do the right thing.
For what it's worth, I think putting a warning on your post is a little patronising, I am the DW who caught her H having an affair and I am in the process of divorce - that doesn't mean to say that I judge everyone who has affairs or get angry or upset at certain topics, I can still offer advice/my opinion. I feel it was more for your benefit to keep away those who may flame you which was proven up thread when you pointed your warning out to another poster.