yes, she's having an affair, she's all about herself lately, and as such, the kids feelings just aren't at the forefront of her thought process.
The fb thing will work, she mentions that you will be nice to the next woman you're with to make you feel better, of course she doesn't sound jealous when she says it, if you were to do something than she would be jealous.
The backrub thing I'm guessing happened after her questioning all the women on your fb page.
She was tagging you, marking her territory. I'm sure the backrub she gave you was more than just a clinical rub, she put a little effort into it and you enjoyed it I'm sure. If that happens again, have some fun with her, you may have had an opportunity to be intimate with her, don't hold back next time, be exciting and unexpected, throw a wrench into the plans.
She also got mad after your backrub incident because she went, maybe hooked up with the other guy, she got mad because maybe she felt guilty as if almost cheating on the OM with you.
