Older brother doesnt like his friend talking to me, but doesnt tell that to his face.Whats going on?

My elder brother who is (22), doesnt like his best friend (22) talking to me (19F) and this issue seemed to have started recently as he never had any problems with his friends talking to me as a general rule.Now his best friend is another story, hes like a brother to me, very friendly,calls me lil sister and hangs around with my brother and me at college.

The problem began when one day my brother asked my opinion about ” who is the most good looking guy in collg”.I was just being honest with him and told him that my friends think that his best friend is kinodff cute.My brother kindoff took my comments badly and said, whats so great in him in an almost offended tone.I told him, I dont know, just heard my friends talk about him. Come to think of it, hes tallish, like 6.2,friendly,good looking and popular with women.

Also, after this incident, whenever his friend talks to me, I notice my brother squirming in his seat , and can see hes not happy. First off, I dont know why hes angry that his Best friend is good looking, secondly he can always tell his buddy if he doesnt like him chatting to me.But he doesnt say that to his face.What could be happening here?