Boyfriend accusing me of talking to his brother

It’s literally Christmas Day and I got into an argument with my boyfriend bc he said I was being “too friendly” with his 19yo brother… I’m 26. We were having conversations about food, sports, and his girlfriend. He swears up and down I was being too friendly with him and shouldn’t have kept a conversation going on for that long.. he even swears I was checking out his brother (which I most definitely was not) and from now on I shouldn’t be conversing with him….. thoughts?