hi and welcome,
Is your wife being treated for her mental issues ?
Are you saying she's been practicing poly or non monogamy for you entire marriage? or like you just the past 5.
Perhaps the stress of the move, increased work load relating to the kids ( school delivery) , upheaval with the kitchen ( generally the biggest stress-or in home remodeling) have pushed things over the edge.
Maybe try to reduce those or if she feels you have dropped the ball in your relationship with her try to identify what it is specifically and pick it up.
She might view your running off to have fun with your lover as escapism or jumping ship.....unfair or something like that.