"Be careful. Him talking about asking the hotel for CCTV proof is deliberately misleading you; no place saves 3 years of CCTV. He knows he can't provide this but it makes him sound plausible. That, to me, makes him seem more suspicious."
This is a prime example of some of the frankly awful commentary and advice on this thread. What would you do, if your partner walked in one day and accused you of cheating on a specific date three years ago, if you were innocent of the charge?
I suspect you'd be frantic. I suspect you'd instinctively know that there's basically almost no way to prove you didn't. I suspect you'd look for the first thing you could think of, in a panic, and grasp at that - in this case CCTV.
Your husband is not and should not be on trial here. He has done nothing wrong. You have no evidence that he has done anything wrong except the anonymous word of someone who has set out to cause him and you pain.
On the basis of the terrible advice you have been given by some people on this thread, you have accused him, and you haven't even done him the courtesy of telling him why, or what, you suspect. He is now supposed to prove a negative which, unless he videotapes his every move and stores it all for three years, he cannot.
Can't you see that you have put him, and you, into a no-win situation? Can't you see that whoever sent you that message is sitting back and laughing at the hurt they have caused you both? And here you are listening to an army of Sherlock Holmes wannabes telling you to put your husband on what is in essence a show trial for their own entertainment.
You started off in this thread as the victim of a horrible and nasty thing. You are now doing a horrible and nasty thing to your husband and you should stop.