Of course he talks about you with his mates when you're not there. He does it in front of you so why wouldn't he? It's as though you've been designated as the person they can see as 'less than them' and all laugh at and degrade. I know exactly what you mean when you say they're not doing it in a horrible way, they're having a laugh. That's what they all say. And then it's your fault for not finding it funny, they're only having a laugh and you're just some boring old sourpuss if you don't like it. It's a way of shutting you up. You can't defend yourself against it, can you? You either have to sit there and be the butt of degrading jokes or be mocked and told you can't take a joke if you callenge it. You can't win because they don't give a shit about how you feel. They think you only exist for their entertainment.
I'm around the same age as you, and so are my husband and his friends. They're all normal men. Mainly tradesmen or work in shops etc and would be described as typically 'Blokey', though not my husband so much. They can be really crude, they can over share and a couple of them aren't the brightest. I have heard them discussing sex in general terms and making rude jokes. Nothing offensive, but adult humour. Never ever about their girlfriends or wives. That is totally off limits. They are people they love and respect, not the butt of a joke.
They honestly sound like teenage boys. I'd want nothing to do with any of them. I know plenty of men who don't ever behave like this. I remember my first boyfriend making a comment about my arse to one of my male friends when he was drunk. It made me feel so angry and humiliated. My male friend looked very awkward as he didn't see me in that way. I was very angry and told my boyfriend to never, ever do that again. He didn't. He was only 17 and quickly learnt that it's not ok. Your partner is an adult and still doesn't get this. He's not even trying to get it, he just wants you to shut up and do as you're told. When you say that he says you should be happy he finds you so attractive... Are you? Does he way he treats you make you feel happy? You don't come across as happy at all. You sound as though you've accepted this is as good as it gets for you. You're missing out on the chance of happiness, self respect and feeling relaxed in your own home. And in the future the chance of a loving, respectful relationship with a real man who actually values your opinion, thinks you're special and amazing and wants to make you feel good. Not using your body for his own sexual desires. Nothing like the pathetic excuse for a man you're dealing with right now.
You sound so... passive and accepting. It's really upsetting. You need to start feeling angry at being treated this way. You know it's not right or you wouldn't have started this thread. I'm sure your mom instincts would kick in if this was happening to your daughter and you would be filled with rage. You are just as precious as her. This is a really long reply because your situation is bothering me and I don't even know you. If I were one of your friends, I'd do whatever I could to help you get away from this.
And don't think that it's not that bad because he doesn't hit you. One of my friends lived in a women's refuge for a while with her baby after she ran away from her abusive husband. He didn't hit her either, but still controlled and abused her in many ways.
One last thing - please don't let him have any naked photos of you or videos of sexual acts because he sounds like the sort of man who would show them to other people.