Your problem isn’t strange at all, or even that uncommon, but it is a serious problem. And to be clear, it is your problem not hers. If she wanted to date her friend of six years she would, but she is dating you. It is unfair to expect her to have only female friends, but now your jealousy is beginning to extend to them as well. This is not a good sign.
You state that she is honest and trustworthy — so you know the problem is your own insecurity, and perhaps, lack of confidence or self-esteem. You really need to examine where your feelings come from before you drive her away. If she has done nothing wrong, yet you don’t trust her, she will eventually get tired of this and move on. Teen relationships can be very emotional and very intense but these intense feelings can sometimes lead to negative choices, such as controlling or aggressive behavior.
I would suggest that you research teenage jealousy for some tips on reeling your feelings back in. If you continue to struggle, it would be helpful to seek the help of a therapist.
All the best,
Dr. Holly Counts