<human>: Can you condense the text into a few key points?

I[22 F] have been dating my SO, Jason[24 M] for about 6 months now, and everything has been going great. He's amazing, funny, smart, attractive, anything I could ever hope for in a man. However, there is one red flag that keeps popping up in our relationship: Carmen[24 F]. 

Carmen and Jason met in high school and dated. They lost their virginities to each other. Eventually, she cheated on him and they broke it off, however remain very close friends to this day. Not only are they close friends, but they continued to hook up on and off throughout college and beyond. 

Carmen always wanted to rekindle the romantic side of the relationship, Jason was always adamant that he wanted to keep it purely physical. Eventually, Jason broke off everything that was happening between them, and it crushed Carmen. He met me three weeks later. 

I, obviously am not to thrilled with the dynamic I have found myself in. She obviously still has feelings for him that have not subsided in the last 8 years they've known each other. Recently, they had a discussion and rekindled their friendship, but with the boundary of my relationship with him in mind. 

I am happy he didn't lose a long-term friend, however, their relationship makes me very uncomfortable. To make matters worse, his friend group is leaving for a three-day booze fueled camping trip without cell service that I will not be attending. I am worried something might happen. 

Am I justified in feeling conflicted about their relationship? I would never be the one to tell him who he can and cannot be friends with, but having a girl around all the time that he has almost a decade's worth of history with makes me uncomfortable. How can I bring this up without sounding accusatory?
<bot>: Boyfriend of 6 months has a female friend that he has had almost a decade's worth of sexual and romantic history with. How can I best bring up my concerns about her without sounding like the crazy psycho I feel like?