I hope you don't believe it, because it's bollocks.
"getting it thrown back in his face" - given they are friends and have already snogged, she's hardly likely to run around saying "uuurgh, Adam asked me out" like an immature teen. She might say a simple no, which is hardly the same thing.
"the woman never does" - Crap.
"she will happily keep shagging the married guy" - as noted above, she was cornered by the married guy who turned up to move in without asking. Hardly "happily shagging"
" if he didn't well - she wouldn't." - So what? No one is obliged to be in a serious relationship. After the death of her husband, she didn't want to be in another relationship as he was the love of her life. She only wanted no-strings-attached. That's completely up to her, and would be whatever the reasons for wanting to stay NSA.
She opened up to him about not wanting to be in a relationship and the next thing he did was push her into one "for her own good" - oh, and in his own self-interest, he was hardly encouraging her to make a go of it with Jamie or any other guy.
And she did say she'd like him to stay living across the hall - that's quite a big "out there" statement given he'd just bought a house for him and his son. He could easily and understandably have said 'no' to that (or thrown it back in her face, to use your parlance)
Things to do now, but sheesh, you have a grim view of relationships. I'm done.