Me and my boyfriend are having an argument

He is upset About some clothes I had on, it was a skirt and and T-shirt and he has a problem with it because he feels like o want other dudes to look at me. I told him that he is insecure. I feel like if he trust me I can wear anything he also feels like I don't know how to fix situations when we argue and sorry isn't enough. I guess my question is how do I avoid this? How do I make him stop feeling insecure and comfort him better?