How should I deal with a girl im dating not wanting me around her bf?

I've been dating this girl for 3 months. She's in a open relationship with her boyfriend. It's long distance because they go to different colleges. Their relationship has been going on for 2 years. I've met the boyfriend, he seems like a nice guy. He knows about me and has no problem with it. He's just happy that his girlfriend is happy. I've not had a problem with them seeing each other until recently. She had him come up to visit her and they spent the whole weekend together. I wanted to spend time with her but she told me she wanted to just be with her bf that weekend. I was pretty disappointed, so I told her how I felt. She got upset and told me that she was just trying to make time for her bf because they haven't seen each other in awhile. I told her that it was bullshit that she couldn't make even a little time for me when he came into town. She got mad and told me that I had no right to question her on how she spends her time with her boyfriend. Plus I had no right to complain because she spends all her week days with me. She was right, but I still felt upset that I couldn't spend time with her when her boyfriend visited. How should I approach this issue?