This is my response to what I understanmd of this situation. You don't necessarily have to agree with what I think and say, and thats okay. I hope this is helpful anyway.
I feel that he should have a right to say what he thinks, but if he is aware of the affect he has on you by saying so, he could have chosen to acknowledge that and keep quiet as to not hurt you. But even so, he should be comfortable voicing his feelings in any way [appropriate]. But if he wasn't aware, then I personally don't feel it was his fault for truthfully saying that he's naturally attracted to others there. Your insecurity limits your boyfriend's freedom of expression (in this case, freely saying who he's attracted to, as it's not his fault for having those feelings anyway), which is what may have been the thing that fustrated him - that you may have made it feel like it's his fault for being attracted to other people because you can't stand it yourself (/ie feel insecure about it). But it's good that you realise people in a relationship can be attracted to others, as that is part of being human. It's very helpful to try and communicate and try and understand his point of view first. By showing your awareness of his side, you could give him a chance to see your reasoning behind your side too. Then yu can offer to discuss what can be done about it and work together as a team to help you grow.
Personal growth is a part of what relationships are about.
Also, it's completely okay to feel this way. I hope you grow to feel more secure about yourself.