one last thing here.....
If you are feeling inadequate and comparing yourself I would suggest that you get out there and find your life for YOU, not relying on anyone else's agenda.
My husband had a hard time for a time until he realized that his jealousy and discomfort was out of not getting on with his private life and staying connected with himself. He has come leaps and bounds since then. He is confident, self assured and has the ability to love himself first before anyone else.
Perhaps reassessing your own life and where you want to be going with it will be beneficial. Nothing like a little "three's a crowd" action to make me look at my stuff and get my act together, get connected to myself and get moving again.
Maybe it's time for her to leave your house so you can get back on track and pull your family back together before moving forward with her in your lives? Your family should always come first as far as I am concerned.... if your kids are negatively feeling the affects of this, that isn't fair to them. Their comfort is the most important thing and that directly comes from the two of you.