I thought he was different

Today at school my boyfriend and I were sitting on the ground waiting for buses and my cuts were exposed because i had my sleeves rolled up. He pulled my sleeves down and i said to him that i didn't care i am not ashamed of them and pulled my sleeve back up. Then he pulled my sleeve down again and said that he was ashamed of them. I left my sleeve down after that and then our bus pulled up.
I'm not sure why he is so ashamed of them but he hates them and it is such a sore point with him so i never bring it up.
I want him to understand but he never does.
I just felt really down after that :(