I have a -very well-thumbed-- copy of Not Just Friends. And an ExH who did indeed cross that line and is hence now my ex.
So I am frequently in the suspicious side of the fence.
But it seems no matter what questions posters ask the OP, all her answers are wrong.
Does he find her attractive?
No, he says he doesn't.
Ooh, red herring, he SAYS he doesn't = they all say that
Is she attractive?
No, I would objectively say I am the more attractive.
Ooh, do you have a very high opinion of yourself?
What's your relationship with her DH like?
Good, we spark and enjoy each other's company. In fact, I'd say there is more chemistry between him and me than between my DH and her.
Ooh, so you have chemistry and tension. Not good, op.
I just feel it's all a bit ... baiting to the op. She's trying to fathom why her friend has subtly stopped the conversations where she has a give-out about her H. The four have become friends. And friends don't like hearing other friends having a bitch in private and then going out as a foursome.
Despite all my overly-spidery spidey senses, I say the dynamic has changed but that does not imply furtive attraction, and I think it is fuelling the op's discomfort, without foundation. She seems pretty grounded and self-aware to me.