When you realised, you never finished your post.

If you can't stomach it, it's unlikely to change over time with this constant reminder of what he did.
More over it isn't the kids fault, if you plan on hanging around you will have to deal with this child eventually.
Can you see yourself able to be a step parent to them without feeling hurt or bitter. Because try as you might kids spot this stuff, no matter how hard you try.

Really do wish you all the best.