Coincidentally, someone else on the forum is having somewhat similar problems.
I really do not understand the situation, but I can hazard a guess.
Maybe this girl simply realised that she was no longer in love with you, but knew that she still cared for you and still remembered the good times.
This might explain why she has moved on to a new romantic partner, but still values your friendship & company.
Whether you will be able to accept this change in your relationship is another matter. It could be very difficult emotionally for you.
If both she and you want honesty, then I think that you need to talk this out fully.
Good luck.
