Meg - I think you are doing quite well despite how heavy a burden your heart is carrying.
I'm glad you've clearly established your boundaries - now make sure you follow through. Do not answer every text, email, phone call. Don't make yourself so available.
I agree with others that your situation isn't going to resolve quickly but I see that all hope is not lost between you and your H. Who knows... when Meg sees who Meg can really be it may be your H begging and pleading for your attention because Meg is complete being Meg.
I will continue to IMPLORE you - and I will do this ENDLESSLY. Stop getting your children in the middle... EVEN YOUR ADULT CHILDREN.
Remember when all is said and done what ever happens bio dad or not this is who your SD sees as her dad... and you are her mom in her eyes. Do not do anything to jeopardize those relationships. Of course your SD is entitled to her opinion. And you can simply state you appreciate her support and understanding that this is a difficult time but no matter what he is always her dad.
Take the high road. Do ever be in a position where your SD may say to anyone that you told her she should tell her dad... of course that would be taken out of context but there it is.
This is the reason that the book states to do not enlist the help of friends or family. Do not be a catalyst that may trigger a fallout between a dad and daughter. You do not want to be that person.
Yes... I know she came to you and told you her thoughts of her own accord... WHAT AN EGO BOOST for you. But make no suggestions to her that she should take that thought to her father. If she ever does it should be because she genuinely wanted to and then she would never say... I was talking to Meg and she told me to tell you this. Can you see how this could be played out?
Your children - minor or adult should only know that they are loved and supported by both parents. Maybe in your book or the book of most parents your H isn't top notch... but he is still their dad. AND, if he took in a child that wasn't his bio one and loved her the same as the others I think that speaks that he does somewhere have a good side.
And, while I don't want to down play any possible porn addiction because that is a real thing... a lot of men watch porn. My husband does... it never bothers me... when he is bored he tends to watch it more. Maybe your husband is truly addicted... but maybe he is just bored and lonely looking for an ego boost? However, maybe its time he get his own google account so you aren't bombarded or left to snoop on his behavior. Its easy enough to get a google account.