In my opinion, that ever happened 'before' you married is irrelevant. Certainly sounds to me that you are more concerned that he "may" have slept with her one last time, before he got married and he may very well have as well, final goodbye to any other woman and are concerned he would cheat on you now..
If he does and you are not happy with that, walk..
Sitting around and worrying about it for the rest of your life will put such a rift into your relationship that you won't have a relationship to work with in any event and so, it will be over anyway.
Jealousy of a woman scorned is what this is about. Obviously she needs help, she's covering her tracks with all of a sudden having a thyroid issue, in one of her emails to him as to why she stalked, sent emails constantly and if you read what she wrote about your looks
Then, she knew she was a fling, a passing thing, not marriage material. Why do you think she emailed you
He married you... Let the past live where it belongs.