Oh, yeah, I also wanted to say to your H, if it's only friendship, then it should be not such a big deal to end it. Plenty of potential cyber friends here!!! And your W has hurt enough - she (you, Lisa) shouldn't have to have any more pain from her H contacting the OW.
Not to minimize how difficult it might be for your H to do this - I know it can be hard when you have had things in your M that were not keeping you feeling safe/loved/desired, but, as I said, I sure learned a lot about myself when I cut off contact with OM and faced the demons that were left over.
Don't know if this is great DBing or not, but thought I'd throw it out for consideration...GOOD LUCK!