Good for sex, harmful for relationship?

I discovered my new kink last night. My boyfriend... (wait for it)... having sex with my friends. Now hold up. I should clarify I don't mean actual sex. I'm a monogamous person, I don't want him touching anyone. I mean the IDEA of him touching one of my friends. I mean, it's the sort of kink I hear about and then think "Jesus, how can some women be into that? I'd be crying!" Well, turns out I am. We had an extremely new experience. It was dirty talk, we got into it. He told me to describe him having sex with one of my friends. At first I was shocked. Then it went on and it was really good. I'm not trying to be TMI, but it was some reallllly good sexting. I came very hard. Well anyways. Afterwards my anxiety sets in. I mean, he was talking about having sex with her, too! He even screenshotted the dirty talk! Does that means he's now getting off to my friends? 
 Let's just say, it was NO BUENO. This was definitely one of the BEST sexy talks we've EVER had, but maybe this is one of those kinks that will damage the relationship and my self esteem. I WISH I could say I could keep my regular feelings and sex feelingsseparate, but I can't promise that! I mean I think all that talking about how much bigger my friend's tits are will become present when it's not so sexy. I don't need insecurities or problems trusting him. But now I know he probably wants to fuck my friend. The kink feels so good but do you think it's just too risky to continue? I could really use advice or stories from people who have experienced something similar.