Many years ago OP I was an OW, in a relationship with a senior colleague. It ended a long time ago, he’s still married, & we have worked together ever since. I do not have any romantic or sexual feelings or interaction with him. I mean I get on with him ok at work, there’s no issue about that, but that’s it. (I have a very happy relationship now with a lovely man who I know would not have an affair, ever.)
I am aware- through work- that since his affair with me, my previous affair partner has had 2 more work affairs. One of them is ongoing & is with someone who I think is vulnerable, a single mother who adores him. I feel very sorry for her.
People can change (I recently commented on a thread about that- my lovely current partner was a complete tit until becoming a father) but this isn’t a case of someone being irresponsible when young. Your husband is almost 60. He already knows the responsibility of fatherhood & marriage. If anything, it sounds as though he has changed to become a more self indulgent, selfish person.
I think you should consider the very strong possibility that it doesn’t matter whether you manage to stop contact with the OW: because there will be more women, in more offices, & potentially more lies. Your rage towards her is understandable, but very misdirected. The issue is your man, & the selfish, self-pitying person he has become. You deserve better.