...he is defiant about continuing to see her. I had another confrontation with him about it tonight, when I realized he was on his way to a date with her.
Now for the additional wrench that's been thrown into this mess, he has just been diagnosed with a serious medical issue which may require chemotherapy. His only sibling (who I'm close to and is the only person I've told about his affair) has also just been diagnosed with breast cancer. I'm torn about whether to wait to expose his affair until we have more information about his medical issues, because they may end up resulting in a forced separation between he and his affair partner. Also, he's leaving in a few days to spend 2 weeks with his sister prior to her breast cancer surgery.
I had a session with Dr Harley last week and we talked in generalities about exposure, but at the time I wasn't sure whether my husband was going to stop seeing his AP, but as of tonight I have his answer. When I confronted him again tonight he told me I was driving him away by doing so.
Welcome to MB. This is a horrible situation to be in, and I'm sorry to read about it.
From what you've written, now that your husband has admitted the affair, he is making no movements towards ending it. Indeed, he is "defiant about continuing to see her". He is willing to break up his marriage over this affair.
As I understand it, you're asking whether the potential separation that your husband's issue might cause might obviate the need for exposure. And you're asking the same question over his sister's health issue: will the fact that he will be with his sister, and therefore unable to see his affair partner, mean that the affair will not continue for those weeks and you can avoid exposure?
I'm sorry, but the need to expose the affair immediately is not affected by either his or his sister's health conditions. Even if we assume the worst - that your husband will need chemotherapy - that does not mean he hasn't already had an affair, and it does not mean that he will not continue having it. The reasons for exposure as just as valid, whether he ends up needing chemotherapy or not.
The same goes for his sister's health; I cannot see why her sad circumstances (which I'm very sorry to hear about) and his visiting her mean that the affair will end. There is no link between those two things at all.
Additionally, I warn you to be careful because he might be
more able to see his affair partner while he is staying with his sister. Obviously, I don't know the details, but it puzzles me that he is will be staying with her for two week BEFORE her surgery. The prospect of surgery is daunting, but why would anyone need someone to stay with them for so long before it? Maybe the night before, but for two weeks? What will he do for her? I should have thought that it was much more necessary for her to have him stay with her for two weeks AFTER the surgery. Breast cancer surgery often involves removing some lymph nodes, and this affects the use of the arm. It is major surgery. She will need help with housework, shopping and cooking AFTER the surgery. Have you spoken to her about the visit, and are you sure it is as he describes it?
You have a gift in the fact that OW has an ex who might be ticked that your H has been having sex in the house while his children are there. You need to expose to him immediately, and recommend that he tells his children. You also need to expose to your husband's family, asking them to put pressure on him to stop the affair, and to your own, asking for support.
You also need to prepare for Plan B, which you should move into this week. Has Steve Harley spoken to you about this?
How long have you been married? Do you have children together? What ages?