I agree I think there is someone else. If I were you I'd hit hard and fast. Figure out how to use this to get full custody of your son and file. Or get her to agree to that in the separation agreement. Do not pay her one penny more than you have to. If you think you can nice her back you can't. The part where she can't afford her new and shiny life isn't your problem anymore. She's said she's done so believe her.
My WAH talked me out of doing a separation agreement but that was only because he knew he'd have to pay me more than he wanted to. WAH has always been short sighted so yes I allowed him to pay me less child support than he should have been paying. Financially it was in his best interest to go ahead file while I was still hopeful. I would have accepted a lower alimony amount in an attempt to nice him back now or sometime in the future.