if he wants you to wear one, he doesn't think you're fat. if you think you are, dont wear one. i dont know if thats actually fat or not, but like i said, if you think you are, then dont wear one. he's not in control of your body, you are
You sound like a normal healthy weight to me :) Don't worry about being fat because you aren't. I'm sure your boyfriend just thinks you have a wonderful body and would like to see you in one so take that as a good thing that he adores you! But you're the one that would be wearing it and if you're not comfortable or insecure about your body don't make it worse by wearing something you don't like just to please somebody else. The most important thing is you feel good about yourself and I'm pretty small and much prefer being in a swimsuit myself.
Wear whatever you like and feel best in and don't worry about your weight! You sound like you're a great weight :)