I agree that a boundary needs to be set that it's not OK to have friends of the opposite-sex that you are alone with. This is really the only case of that and the fact that she hid it tells me she knows my stance on it and chose to do it anyways.
I'm going to look into the No Mr Nice Guy book, but I am not a doormat now. As soon as I found out about the OM I confronted her about it and began my way over the top snooping.
I'm trying to find the right balance of not being a doormat but also being more attentive to her needs and doing "nicer" things. Here's an example: we just moved and had a bunch of heavy items in the hallway that need to be moved so the furniture people could get through later today. I moved them without prompting when she wasn't home this morning. That is something that I would have had to be prompted to do a few months ago. I also took her out to breakfast unexpectedly after we dropped the kids off at school. That's something that I normally would not have done because I don't really care for it, although she enjoys it.
