Boyfriend suggested a ?

My bf of 2 yrs said that one of his fantasies would be seeing me getting it on with another girl (having a ). He stated his viewpoint, I stated mine. I dont like the idea of sharing myself or my bf with anyone. He doesnt understand this, saying that if we're secure in our relationship that the wont do damage. Ive never had a guy in my life even suggest a and I believe out of respect (I think Im a decent kind of girl). My bf says its b/c no guy has had the to ask. I believe in having a healthy, monogamous relationship. The thought of seeing another person in our bed pisses me off. Im just offended that he thinks its not a big deal to suggest a or that it would be cool. Im not judging others who do it, but its not my thing. Am I wrong for feeling this way? What does this say about his character? He says he loves me very much and as soon as I start feeling hurt about the subject, he backs off.