Reen the battlefield is your mind.
If you want to forget about this than just drop it and move forward and live your life.
However, you just said, "then I think well here goes....another attempt to bury it until it comes back again sometime in the future. I don't have any control over any of this or my emotions".
This is obviously still (and has been bothering) you for many years. This is no way to live. You obviously just want to know the truth. So your gut instinct was right that you knew she lied to you way back when.
Your gut (your mind) isn't going to just drop this. It WILL continue to linger and nag at you until you feel like you have the truth.
This is just my opinion. I think deep down in your soul you think that not only did your wife lie to you about this guy/date/night but that she also had sex with him that night and that's why she's lied about it all these years.
You want the truth but your fear of finally knowing what you've thought happened twenty yrs ago is keeping you from opening Pandora's box (which is certainly understandable). However not knowing WILL continue to nag at you.
So you're damned if you do damned if you don't.
If you have the relationship with your wife that you think you have than she should be willing to give you the truth since this is (and has been.....and more importantly will continue to) bother you.
She just randomly brought it up recently after twenty yrs?
If she loves you than she should be willing to do whatever you need in order to settle this once and for all in your mind or it's going to continue to fester and come back up time and time again.
If it were me I would ask her if she'd be willing to take a polygraph? If she says "yes" schedule it. If she says "no" ask her why not? If nothing happened why the need to lie about it then but more importantly why the need to lie about it for TWENTY yrs and why the need to randomly bring it up recently?
Ask yourself this, if she fails, and it comes out that she did indeed have sex with this guy twenty yrs ago, would you leave her? What would this do to your marriage?
If it's as good as you think it is (the marriage) than why would learning the truth about what she did twenty yrs ago damage it? Your marital foundation is truly solid as rock or it's not and if it's not than that means the two of you have been lying/pretending with one another. In reality.....living a lie.
The results of a polygraph come out one of two ways.
She's telling the truth and that nothing happened at which point the nagging thoughts in your soul are put to bed and you rest comfortably knowing that you didn't let FEAR keep you from confronting this situation.
Or.
It's determined she was lying and she did have sex with this guy twenty yrs ago. At which point you'll have the truth, and the two of you can start addressing the elephant that's been in your relationship for twenty yrs.
Yes your fear will now have been determined to be true, but Reen it doesn't have to mean your relationship with this woman is over. It will hopefully start the process of getting your marriage/relationship on a TRUE SOLID FOUNDATION and not on lies and deceit.
One could certainly understand why she would keep this secret all of these yrs (if it is indeed true) as she feared you would leave her. Is this really the way the two of you want to live your life together?
Her having to keep this huge lie fearing that if the truth is ever revealed her world is going to blow up and you always wondering what really happened and more importantly why your wife doesn't trust you enough to tell you the truth so that she can help you settle your restless spirit.
Assure her that you are NOT going anywhere no matter what.
Even if she lied.
She either trusts you enough to tell you the truth and if she doesn't why continue on with this charade of a marriage?
If she says she's telling you the truth (and thus why the need for a poly....that her word she be good enough) I would look her in the eyes and tell her she herself has told you she's lied about this situation and if it were anything else but this specific topic you would believe her.
That said the only thing you can think of to get the peace you're seeking from this is for her to take a poly. If she is unwilling to do this then Reen (if it were me) I would have my answer.
Knowing the damage it could do if she isn't willing to take the poly she's going to double down and not be willing to do something that you desperately need from her in order to finally be at peace?
Reen my comments are ALL based on you saying "another attempt to bury it until it comes back again". So obviously you're not good with where (and how) this is being addressed.
Have the courage to face your fear.
2nd Timothy 1:7 says the following:
"For God has not given us a spirit of fear, but of power and of love and of a sound mind".
Only you can answer this Reen but does this scripture ring true with you?
I wish you well but more importantly I will pray for you (for wisdom, guidance, and courage to do what you need for peace).