Hello Supersaint. I think talking to him is essential, so I'm glad you've carved out some time. I come at this from the perspective too that if we're faced with any major decision in life, it makes sense to have all the information. So in your shoes, I would want to know everything.
You might not be strong enough just yet to hear all the sexual details, but if you do rebuild, I recommend that you know everything. There are two reasons for this; your imagination will be worse than the reality and secondly, you cannot even start a path to forgiveness until you know everything there is to forgive.
I would set some ground rules for your chat. You will doubtlessly have moments of intense anger and although he needs to know you are righteously angry, it often gets in the way of listening. Anger is fine if it doesn't harm you or others and in this case, it might harm you if you lose out on some information. So if you feel yourself becoming furious, just take a brief adjournment.
Secondly, in the immediate aftermath of a discovery, many lies are told. Some of these will be lies to minimise his culpability, some will be to minimise your hurt and there will also be numerous lies of omission.
It would therefore help if you set a groundrule request that to every question, he affords you the respect of the truth, however painful to you and however damaging to him. He should also show you copies of E mails, texts or any letters that passed between them.
Mixed in with all your conflicting emotions, there will be some loss of safety and a need to reconstruct the story of your life for the past 18 months. It is not unusual at all for people to want to cross-reference phone bills and diaries and reframe the period in time when they were being deceived.
I would be very much in listening mode, without giving any judgements or conclusions. However, what he has never heard yet is the story of the affair from your perspective. Unless he was a complete compartmentaliser, I expect you have seen some changed and worsening behaviour, apart from in recent times after he ended the affair.
Do tell him what life was like for you, living with someone who was harbouring such a secret. This is often something of a shock, because while in the grip of the insanity that is an affair, people lose their ability to see the true impact of their behaviour. As a general rule, there is often far more to forgive than infidelity.
Good luck and I'm glad you're going to get some answers. I can't imagine how you've got through this week, so you are doing incredibly well. Do update when you get the chance.