Infidelity Support Group
Any relationship in which one partner engages willfully in sexual relations with another outside of the partnership is considered to have experienced infidelity. This breach of trust is often traumatizing for the faithful partner as well as the relationship, and support is often needed to heal emotionally and to decide whether or not the relationship should continue after...
"I don't remember" is a standard cheater method to not deal with the fallout of their cheating and betrayal.
You and your husband should read the "musts" of rebuilding, which clearly states that the cheater needs to answer all questions honestly.
I will bump the article for you.
Trust your instincts. I wish I had have... If your instincts tell you he is lying, he is. Don't ignore them.
And honestly, a lot of men don't remember bunches of minor details like that. I can honestly say if my W asked me, "What did you say to your son when you were at the store with him last year in May?" There is a very good chance I wouldn't know that. So a lot depends on the details you're wanting.
That said, cheaters do use that line, and it is hard to tell whether they are telling the truth or not. The situation being what it is, you have to assume they really remember but don't want to tell you. Unless you feel like you are getting all the important details. Like, he had sex with her about 5 times, but to know dates, times, places, he may only remember some of it. If he's telling you they had sex, why would he want to withhold info on it? Unless it is info about the OW and he is protecting her. But how long, etc.? I don't get why he wouldn't tell that if he knew. After all, he's already told you the bad part, that he did it (maybe after extracting it from him).
But some men are more closed up than others too. Doesn't want to give out any more info than they absolutely feel they have to. Problem is, that's a sure road to the end of the marriage.
They have to be open about everything and answer any and all questions.
And the BS needs to work to make sure he/she only asks those questions they really need to know. Some details are better left unsaid.