Although sex played a big role was not the reason for continuing the affair.
1) The fact you admit sex played a big role in the affair will be crippling for him, no doubt. Many in your position downplay the sexual component, which only frustrates and causes further distrust, as the waywards actions often speak otherwise. As crazy as it sounds, your truthfulness here will earn you some respect.If you say it played no role in the continuance of the affair, you will be challenged, so be prepared to answer how or why you stayed with the sex then.
So while your thoughts or reasoning may be centered around the excitement, etc., he may associate the excitement to being "sexual excitement". Many wives underestimate the impact the sexual infidelity has on their husbands and it takes them a while to process this. Whereas, if you acknowledge this up front and place it in its proper context, it will allow you to communicate in his language earlier in the confession/post recovery discussions, as well as allow you to empathize more deeply than you already seem to be.
2) It would be helpful if you can come up with some answers in anticipation of his questions. One of his first questions will be why, when, where, etc. To be practical here, your why's will not change anything. He will ask it over and over, as nothing you say will make sense. It's just a knee jerk response question as he begins processing this tragedy.
I'd pay special attention to the questions you can't answer and may respond with a "I don't know". Being able to say, you're working diligently with a mental health professional so that you can supply him with answers to his questions will be meaningful to him.
3) Don't place him in a position where he has to console you. I'm not saying you can't be emotional, but he's the one that will require support.
4) You may have a challenge confessing everything you wish to say, as once things get going, it's easy to forget and omit information. So, it's okay to read from a statement. You'll have many talks, but only one initial confession.
5) In time, he will associate times and places you were with your AP and could/should have been with him. Not sure there's much you can do here except listen without defending and excusing.
6) He may ask you to notify AP's wife and he may want to contact AP to corroborate your story.
7) He will probably ask, what if AP hadn't moved away. Tough one here as you both know the affair would still be going full blast. Nothing you say aside from the truth will fly. Most unfaithful say they were trying to end it for weeks, months, etc. This actually makes it worse in some cases, as it reveals the AP was so irresistible, your best efforts and risks of losing husband and the marriage, were still not enough to pry you from your AP's spell.
You will have to do a massive job of loving him in order for your husband to regain his self worth as a lover and husband to overcome this. Your AP moving away is almost like your husband discovering it on his own, in that it didn't end because of you wanting to be with your husband, but because AP was no longer available. He may see himself in the dreaded fallback option.
8) If possible, he'll not be able to execute simple functions like finding an IC etc. If you can do some of the legwork here, it would help him tremendously.
9) If you have a pastor, schedule a prayer session with him and your husband. If your husband passes on the offer, go anyway. Aside from you or your loved on the verge of death, rarely will you need a higher power more then right now.
10) Needless to say, pour your heart out like you've never done before. If he allows you to get close to him, do so. If he allows you to grasp both of his hands and talk to him eye to eye, do so. Whatever comforts him, do it. Whatever discomforts him, refrain from it and respect his boundaries. It's his time. He makes the rules. You follow them.