Sounds to me like you've made a similar error to that of what most do in a market. You became too attached... "my new gf","3rd date". She's 48 and probably realistic about the long term prospect of a relationship with a 28 yo. She may have JUST wanted some fun with a younger man, or maybe it could have been that when the fun began you were like the bomber .
My mother works in a bank full of middle aged woman, she told me that they're all disgusting. Everytime any new young male starts working there the older woman trip over one another to be first in line. She told me that I wouldn't believe some of things these woman talk about. Long story short anyway, guys tend to go limp in their 40s or 50s and from what I gather, a womans sex drive doesn't die with their partners penis.