My boyfriend told me that he wouldn't mind having a threesome and it really hurt me

Yesterday my boyfriend casually brought up the topic of threesomes, and I was fine with it at first then he started to go on about how he would try it if I wanted, and I was just like WHAT? I was kinda offended tbh at made me feel a little insecure that maybe I don't satisfy him and that he needs another person to help? And what if he enjoys it more with the other person? I told him that I would never consent to that though and that I would be super offended if he ever asked me to join a threesome with him and that If he did I would possible dump him right there and then. He told me that if that how I feel then he wouldn't do it but now it is on my mind that he would actually think of doing that, it's really upset me. I told him that it's just physical and that there's no love involved and he said that's the point? I see sex as something that is shared between lovers, I told him it's pretty much like me going out right now a f***ing some guy and telling hims it's okay cause it was just physical and that he is still the only one I love, anyway I was super upset by the question and actually cried later on because I felt so insecure, later I felt that maybe I overreacted and was over sensitive to the question and that he was just voicing his opinion and I jumped down his throat? What do you think? I'm i overreacting?

P. S We are a gay couple, (two guys)