There's no real answer to the question, why did she betray you. I don't think anyone can precisely tell you that without asking her why. It does seem she was in love with you and that this was more than platonic on her end. It seems she wanted to push men away from you and keep you to herself. Perhaps she was angry you didn't reciprocate the feelings? The cuddling may have convinced her that the feelings were mutual. But overall, I agree with the others that this friendship was toxic and it's best that it ends. I am glad you are getting help. Time to pick healthier friendships, and ones that don't cross boundaries, if you are hetero. Those can get messy when feelings become involved.