I see what you are getting at, my boyfriend did some photos for a gay magazine; not porn, and did cam shit with his last boyfriend and seems almost proud of it.
It can be annoying and a bother, I think you have to experience it to get it, or maybe just be the type of person who doesn't think that is something to brag about.
It's not even slut shamming, or anything, I've had sex with more guys than my boyfriend, so I actually am a bigger whore. But there is something about being "proud" about doing porn, or modelling that seems really conceited, which can be a very unattractive trait. I think that is what you are getting at, you don't enjoy being with someone that seems almost conceited.
Being proud of yourself, and knowing you are goodlooking...etc are fine, but modesty is all a very attractive quality, and a guy that did porn and doesn't share it not because he is ashamed but because he doesn't want to seem like a self-absorbed jack ass is a much more attractive quality.
I think you are more annoyed that he sent it to friends and is really open about it than he actually did it, and I get that. I don't really have any advice, I just would try to ground him into reality if you can.
My boyfriend learnt very quickly that I'm not the type of guy that is impressed or interested in that type of shit; I'm not a prude I'm open about watching porn and what guys and girls I think are hot with him, but you are more interested in him as a human being than the fact he did shit like that.
You can do that, let him know that, I believe that you can be generally interested and like/love a guy that has qualities you don't like because you like other things about him. I'd just let him know through disinterest that you really aren't impressed with crap like that and that you think bragging about something like that is pretty fucking lame. It doesn't have to affect your relationship, you just need to show that you don't care and aren't interested in those things about him.
Everytime my boyfriend mentioned the cam he did with his boyfriend I tell him anybody that is mildy attractive can do porn, not in a mean way, but in a "I could do that too you aren't special" way. I also imitated the stupid poses he did in the magazine for a couple weeks after he showed me, again not in a mean way, just poking fun. He realized that I'm not impressed by that, and told me I'm the first guy he's dated that hasn't just tried to fuck him, and that's because I actually like him, he is a really funny guy that matches be properly. His tactics of showing off how "hot" he is turns me off, and he realizes that now. I never had to tell him fully, I just acted embarrassed for him when he tried to act proud about everything. I tell him I know he's hot and people want to fuck him and that I don't chase after people and I don't like him because he's hot. If I just thought he was hot I would have fucked him and chucked him; I don't do that but it drove the point home: YOU DON'T NEED TO IMPRESS ME ANYMORE WE ARE ALREADY DATING.