The other woman

Okay I need some help :( I've been seeing a guy and although we are not official on Facebook we call each other our significant other and know our close friends and families. Just taking it slow. He has a friend that's also a woman and they were best friends over the summer. She thought they were more than just friends and he didn't want her that way. She was just another one of the boys. He never flirts with her but we invite her over with our other close friends for parties and such. After she leaves here she'll text him sorry for being annoying sorry I intruded but then will yell at him when he doesn't invite her to hang out with just me and him. I've been accepting. I've been nice. She's afraid I don't like her. I don't know what to do! Please help :(