Yes, you should be upset! Think about it, how would he feel if he knew you were calling other guys handsome or sexy. I say sexy because in mens eyes, sexy is almost as equal to what guys like being called as women do being called beautiful. I did a poll on that, and I thought it would be handsome, but turns out it was sexy haha.
He would be really pissed off that you would do something like that, right? Well then, you should be allowed to get mad when he calls other girls beautiful.
dont be just stay confident and have this on your mind " whatever he throws at you or when he compliments a girls its another good karma" becuase if you threat a woman like crap you know the deal what goes around comes around. stay positive and he will want you more trust me.
I wouldn't worry, don't jump to conclusions, maybe she is just a friend. Just because he said she is beautiful doesn't mean that he is doing something wrong, I tell my friends they are goodlooking all the time, its not in a sexual way. He is probly acting irratated because he feels like you don't trust him and are jumping to conclusions...did you see anything else that made you curious? And just try calmly starting a convo about it...you ccould even say something like dang your right she is beautiful, how do you know her?
My boyfriend calls his female best friend beautiful all the time. They've been best friends far longer than I've known him, so it doesn't bother me. He'll even answer the phone with her saying "Hey beautiful!" It doesn't bother me, but I guess it depends on the situation too
well if he is letting you see it that probably means that he isn't trying to hide anything from you and doesn't mean it in a sexual way. just remember that you're the one he wants to be with, not her, and I'm sure he thinks you are even more special than she is