overboard jealousy

My boyfriend is amazing and is constantly letting me know how much he loves me and how much I mean to him. That being said, I still find myself getting mad if he mentions talking to girls. It's like I go 0 to100 real quick and I get so mad. In my mind those girls are flirting with him and trying to get with him while he just lets it happen. Any tips or suggestions that can help me get over these reactions? I hate that it still happens because he has showed me time and time again that I have nothing to worry about , yet I still go crazy. I still have these images in my head that he might be flirting or doing something. I know he gets along better with girls just because he grew up with only sisters so it's only natural because I grew up with my brothers and naturally get along with guys. I know, i shouldn't get mad if  the same way but it still bothers the SHIT out of me. Any suggestions would greatly be appreciated z