Am i over reacting?

Wassup people i got a interesting situation today and i want to know if you guys and gals can help me out. I'm currently talking to a female whom I've been seeing for a couple months now (5) and things are going good. We make each other laugh enjoy each others company and i find her very sexy which is a plus, this all sounds good but i struggle with one problem that i go back and forth on. She is bisexual, not a problem because i knew this , but she has a friend that she once dated for a bit so there is a Lil bit of history there cool. Now the problem for me is that they are inseparable and me and my girl don't go anywhere. We don't go out to eat, travel nothing. All we do is what your probably thinking...lol. This would be all good for me cause that's what most us guys want anyway, but I'm not a relationship guy and I'm trying to do this and thought they consisted of a lot more than this. This "friend" of hers seem to do everything together from a nice dinner in the city yo family gatherings and I'm supposed to sit back and just believe that there is nothing else going on there. I try not to make it an issue, but i had to bring it to her attention and she swears that they do nothing of the sort yet she agrees that if the shoe was on the other foot she would definitely find a problem. If this is the case and you understand where I'm coming from than why does she get upset when i find it an issue? I have a lot of love for this woman, but at the same time I'm not a fool and can only put up with soo much. Please give your opinions on this issue, what should i do....