am i allowed to be angry?

so i'm sort of in a weird situation with my boyfriend. we've been long distance dating for a bit and we've known each other for over 3 years. today when we were skyping we were talking about old pictures of him that was on his mom's facebook, and there was a picture of him and his ex on there from like a year ago. i laughed about it and was like "i was wondering what she looked like haha" because he had talked so lowly about her personality (she cheated on him). he then said, "she had big tits and a fat ass though". i got angry, but he said "i mean she's very good looking like she's stunning but you're much more stunning and your personality is much better". i'm still very bothered about this and i didn't want to continue arguing because we've never really gotten in a real argument before and i hate fights but it just really bothers me that he said that his ex was "stunning and had big tits and a fat ass". is it okay for me to be angry? or should i just let it go?