Would you be mad???

ok y'all so my love interest is best friends with this girl - which I generally don't have a problem with at all. But when I've spent time around them, like for example we went out for a meal together, they were being really close with eachother the whole time, they go everywhere together, she wears his clothes all the time and she even sleeps at his house. I know he doesn't like her and she doesn't like him, but it's still kinda awkward for me and it's kinda annoying.