Thanks, Kevin. I think you probably hit the nail on the head. I know she has body image issues, though she is quite thin and lovely. I do know some of her past issues. Her father was abusive with her mother and she has confided that he would take her to mistresses' homes when she was younger, so there is that. She has never admitted, but I suspect there may have been some sexual abuse when she was younger...again, it's just a suspicion I have.
I do think that the insecurities/comparing is a big part of the problem as well. And I am sure she knows any worries that her DH would ever leave or that I would leave my DH are irrational she more than likely has thought. I also think that some of it is jealous that he would have feelings for me that are more than just friendship.
Another thing to consider is that she has done things sexually with my DH, with just me and together with both my DH and I. So, she has no problems with that, but the one time it was suggested that I join both her and BF she said that she was uncomfortable with that. So, there are definitely issues there. I don't know if it's a trust issue she has with him, jealousy or both. Other than what he has with me he has never been unfaithful to her.
I will try to be more attentive and more of a friend to her, but we are definitely opposite personalities. She is a people pleaser and cares what others think, whereas I am more of an outspoken type that has a difficulty sugarcoating things.
Even though I am not terribly happy that she prefers things secretive I am not willing to give up my relationship with my BF as I love him very much and don't want to try to go back to being just friends. And as long as everyone else is ok with the current situation is it so bad to continue as is and keep trying in hopes that she comes around? It may not be the way I want things to be, but she is definitely not ready for things to be out in the open.