Rachael, The doormat thread is very helpful and it gives you something to think about.
Now about your friend, it's best not to share what is going on between you and your husband w/her. I get the impression from your posting that she likes to step in and offer free advice on just about everything. You do not need this type of friendship right now and you sure do not need her giving advice to your h. The fewer people that meddle in that little pot of mlc, the better.
Everyone has a viewpoint about whether we are fools for believing in our spouses, but until they walk a mile in our shoes, they need to step back and allow you to make your own decisions as to whether you stay w/him on not. She needs to be focusing on her own situation because it doesn't sound like her situation is any better. You need people who are going to support you...not discourage you.
As for your h, he's depressed and will be for a long time. He needs to work on his issues w/o distraction. Just because he doesn't go to confession doesn't mean he's still in the affair. Many of the mlcers will do the opposite of what they use to do, i.e., in his case, he doesn't go to confession. Some mlcers will stop believing in their faith until they hit bottom. Others who weren't believers pre-mlc, will begin reading the bible and preaching the holy word. So, we can't judge this mlcer's book by its cover.
Hang in there...but do not what's going on w/your friend. She can't help you w/this situation.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.