My SO is uncomfortable with my bisexuality..

I've been with my SO for almost 3yrs now. I was very upfront and open about my bisexuality when we first started dating. He seemed curious about it but it didn't really seem to bother him. I opened up to him about the fact I had dated women in the past and enjoyed it. About two years into dating I brought up the idea of having a woman join us not anytime soon but maybe in the future. Not because I was unsatisfied but because I still find women attractive and thought it would bring us a little closer. Instead he flipped out about it and seems very insecure with the fact I find women attractive. Get very upset if I say anything about women being attractive or talk about them way at all... Is this weird for him to not want something like that? I haven't brought it up again since but it bothers me how he hates the idea so much.