Oh no, I'm not suggesting any man not be nice.....if her can. But I know you seem to have concussion about her being nice in comparison to others. And we don't read a lot about nice WAW's, but it is not as uncommon (from the posts I've read) for the WAH to be nice to the LBW, even when he has OW.
As long as she is showing you respect in your presence, in your home, and in front of your children........and respecting your boundaries, you should conduct yourself with politeness and friendliness, if possible. If you have to compromise with your values, standards, boundaries, and be passive in order to be "nice" to her.......then don't be nice or friendly. It is more important to be firm with her and have her respect. Nothing is more important than your W's respect. Without it, you can never have her true love for a H. A woman cannot love a man with true sexual love without respecting him as a man first.
So by all means, stand your ground, protect your boundaries, and don't be a passive wimp just in order for her to think of you as a nice guy. There are a lot of nice guys out there that a lot of women don't respect.
You didn't do anything wrong. I was just making a comment.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!