Hey O, saw you on GF's thread and wanted to take a look at your sitch. You came to a very wise realization about your reaction to your FIL's A. I used to think the same way and although I have no indication or proof of an A with my H, I feel much differently about the subject since it is a possibility. Until your are in that sitch, I guess it ia hard to see both sides.
At first your H may feel this vindication at being forgiven but the OW's allure will fade and fade fast. Stay strong for you and your sanity. I feel for you as our sitchs are not the same but our life profile is: no kids, M 5yrs, known H for a decade or more...got our bad news in Oct. O, I can see in your post that you can forgive and I don't know how it all works in Australia but hang in there and most importantly KEEP YOUR DIGNITY...save all the other stuff that you need to get out for your Amy punching bag