How long should I keep asking questions about the affair?
No established rules exist for how long any specific recovery step should take. Every situation is different, as are the participants in the process. But here is a truth: it is healthy to move intentionally toward ceasing all conversation about the past affair. Getting to this point takes time: months for most betrayed spouses. But if there is a joint commitment to move forward in the marriage, there needs to be a point at which you decide that conversations about the past are no longer necessary.
I don't mean that you should pretend it never happened or that you can never speak of the affair again. The betrayed partner will continue to feel pain for years and needs to be honest about expressing that pain. But those conversations can focus on the present and future without reverting to more questions about the past.
Here's the truth:
You'll never have a 100% understanding of the affair.
Getting answers to questions about the affair is necessary, but the knowledge learned by the betrayed spouse should focus on the information that helps gain an understanding of the meaning of the affair, not all of the facts of it. In my experience, 90% of all important information is learned quickly once the betrayed spouse commits to honesty. The other 10% won't make a difference in the recovery process. (And if the betrayed spouse still isn't committed to honesty after months, you have a different problem.)
Most betrayed spouses should start letting go of questions before they feel ready. I know some people promote a "ask as much as you want for as long as you want" perspective, and many times they're the same ones who encourage a betrayed spouse to "be as angry as you want for as long as you want." I disagree with both sentiments. Yes, you need to ask questions; lots of them. Yes, you need to express your anger honestly, the whole depth of it. But if you do not move intentionally beyond those two things, you can stay stuck too long... perhaps forever.
Here's what I recommend to betrayed spouses once we've been through a Truth Session (a planned and focused conversation providing honest answers to questions about the affair) and they express a willingness to move forward in the relationship:
For the next few weeks, limit your affair questions to 2-4 times per week, for a limited amount of time that is NOT just before you go to bed. I usually ask the involved spouse to be responsible for ensuring these conversations happen. This behavior begins to reinforce the ability to be self-regulating rather than compulsive.
Between these conversations, write down the questions that come to mind instead of talking about them immediately. Think about each question from the perspective of your future self and ask, “Will the answer to this question help me heal?” When the scheduled talk time arrives, you'll have your questions ready, even though some may not seem as important to you by then.
After a few weeks, cut out one of your talk times or expand the time between them. Continue this reduction every couple of weeks until conversations are limited to once every few weeks.
Eventually, when you are ready, declare, "No more questions about the past; I don't need to know anything else. Let's focus on today and tomorrow."