I think the BI is implying that he is being forced to stay in the marriage by friends and family and she's clinging onto him. And that he's not being faithful to her, she knows it and yet won't still leave him. That's what I got from it.
I so agree with this interpratation, I too think it's Garner and Affleck if you go on Lainey's site and go into archives and read her posts on Garner and Affleck (and Blake - ick!) it definitely fits, this is pretty transparent. Affleck sees himself as a politically knowledgable he at one point hinted that he might run for office, so he sees himself as a sort of expert on policy etc. If you ever see him for example on political talk shows like Bill MAher he sees himself as an authority on all things politics.