>>187 I agree with you about the FWB thing, and that she's definitely more into it than he is... much like the situation with JA, which, keep in mind, went on for a year and a half and only ended after some unknown explosion in Bora Bora (something to do with the photograph? her favoriting tweets about them as a couple? who knows).
Tom the workaholic seems to find someone whose company he enjoys as a friend to some level but isn't what he's looking for in a serious partner, she's willing, they carry on until the woman's level of investment becomes too much or she tries to push him into a bigger commitment, and then it ends. Unless something goes "wrong" there's no reason for Tom to end it - he likely prefers having a thoroughly vetted FWB he feels like he can trust as opposed to casual hookups with people he doesn't know well. Also, when you have a FWB you can more or less rely on regularly scheduled, um, Benefits when you need them.
One more thing, someone (qaz? I think it was you) said something upthread about traveling to Hawaii being too committal for a FWB, but EO has always been a globetrotter, and for someone with her money and resources taking a brief trip out to Hawaii is more like a regular person driving a couple of hours. Even before ISTL she was always flying out to London, Paris, NYC, and other random cities for no particular reason.