itm, you wrote: "the last 19 years have been a complete sham.."
but it wasn't *all* of those years, right? I thought, from what you wrote previously, that the affair only started during your separation. and that before then there were other problems (his drinking) but not infidelity.
and if so, it's not like the *whole* 19 years were a sham. they were problematic, and maybe during the last year or two he was carrying on with ow. but if I understand correctly, then at first your marriage was ok, and it is only in the past few years that he changed. (and it's a shame that he changed like that, but if he is giving you up, then it is his loss!)