It's not normal, and your feelings are right on the money. Any one who wants to keep their marriage together would feel hurt by what he's doing.
I wouldn't put all
the blame on you, or him. Usually there are a lot of things that cause problems and I won't pretend to know all of what plagues your marriage. But, if I were you I would just find out how serious it all is.
feels self-conscious about himself, he could be looking at these sites not to have affairs, but to boost his own self confidence. Is there any way you can make a fake profile, pretend to be someone else, and see how far he takes it?
I don't think my advice is necessarily the best, but if it were me
I would tell him that the marriage is equal: if he can venture out in that department, they so can you. Put your own profile up on the same site he's on. Let him see other men desire YOU. If he wants to look at porn, tell him he can have a turn when you are done looking at other naked men. :P But, that is all mean. It's not nice or productive to be mean.
OH, but as a side note...if he's saying that he's no longer turned on by you, have you asked him the age old question: "what exactly
do you need from me to be good enough?" I mean, simply being "more adventurous" and "loosing 25" may not be specific enough. Hell, I've lost 55 pounds in the last 9 months...but I still have 20 more to go. (pregnancy sucks). Does he want you to be a certain size? Does he want you to be aggresive? Sometimes him just writing a formal paper list is all it takes for him to realize he's being a little too anal. It's one thing to request a few things of our spouses, it's another to say they totally suck. Also, if there is a "check list" and you meet it, and then there are still problems, then something else is the issue.
Last note (sorry this is so long): Just because he wants you to do certain things, does not mean he is exempt from change. If he wants you to loose weight, it is only fair that you give him a list too, like: he do the grocery shopping to avoid temptations. Or, if he wants you to go out of your comfort zone during sex, then take turns: this Friday you play dominatrix and next week he covers the bed in rose petals for you. It's not all a one-way street, and we all have our fantasies.