SO thinks I'm fat..

A few months ago my boyfriend of 3 years told me that I am gaining weight. We talked about it for a little bit and he realized him bringing it up had made me upset. Today he mentioned it again and he said that I gained weight in my stomach and it was unattractive. I thought the way he said it was very rude and I told him that beauty fades and I don't want a guy to only like me for the way I look. And he said I was overreacting and he just kept telling me I need to work out. I got really frustrated with him be used he didn't listen to anything I had to say. I know that I am not fat but I'm not a twig either. I am 5'5' and weigh 140 and I have curves. I don't want to be a tiny model sized girl who starves herself for the approval of others. I just am kinda overwhelmed.