Boyfriend called my sister pretty

So first of all, let me start of by saying that i am aware that i might be overreacting a bit.. so i posted a snap of my sister on my mystory and saw that my boyfriend had screenshotted it. I then asked him why. He goes: " i dunno, she's cute". I've been compared to my sister my entire life and have always been called ugly in comparison, so hearing my boyfriend comment her looks made me cry so bad. I probably sound super dramatic but honestly feels super sad to hear by the one person who you want to only talk about how pretty you are. Anyone else have similar stories? And am i reading too much into this?