Sleeping with others while married isn't about spicing things up, its about a selfish sexual need that just one person can't fulfill.Funny how she tells you monogamy doesn't make sense in a marriage, because I doubt thats what she told you when you all dated and got married to begin with.
After i told her about my one night stands we had great sex and it did get things going.
I am just wondering if someone else has gone down this path and what their experience was. if she wants to sleep with others, for whatever reason she has, then let her and while she is doing that, hand her divorce papers and tell her to have fun. Tell her its unacceptable for her to want to do this to you and your marriage.
If she doesn't care what you say, then you have your answer.
She is wanting her cake and eating it too, doesn't work that way.
If she doesn't care what you say, then tell her since you believe in monogamy and she doesn't, that you have an itch as well, and its called separation papers, and that you feel by her signing it, it will help ease that itch.