Cally-- I'm sorry to hear about this from your H. In my research over the last few weeks, I found information about sexual addiction. It's a very real addiction like drugs and alcohol. One of the effects is to act out with porn, mb, strangers (not that your H is doing that for sure), etc. I don't want to give you any type of false hope but your H sounds like he is a good candidate for it. Check out the site saa.org. If you can get him to C, you might want to discuss it there as well.
If he is an addict, it's something that would NOT be easy to admit to yourself OR your spouse. BUT, another one of the signs is avoiding your spouse for these other activities.
Just wanted to give you some options to consider. You've always been so full of good advice for me!! K