Well five pretty good, and different but not inconsisteny answers above.
Start by looking at your options and results of each.
1. You could leave him. Sounds like you might be leaving someone you really love and for something he did BEFORE (not since) you were even married to him. If you can NOT get past the problem, maybe you should consider this option.
2. You can do what you've been doing. You can brood over it and let it eat away at you from within. You see what that causes; you are now turned off to sex and to him (a fact he has or will pick up on and that will then spiral into much bigger problems that might never be capable of being resolved.
3. You can come to grips with it, as some suggested (directly or indirectly) ... whether by prayer or by counseling or within yourself. This means you get your grieving about it over with ... you can NOT go on grieving over it; it has already taken a toll (on you and on the marriage, probably on him too). This would be the way to keep your husband and your marriage, to bury that "event" and go forward in a mutually loving way. Is this easy to do? Probably not. Especially since you are characterizing it as a "tragic" event. So how would you "bury" it?
The way to "bury" it is to go get counseling with a professional who can help you work past your shock and disappointlment and put it in a more objective and more realistic perspective for you. Someone who could help you see that wanting a "virgin" for a spouse is very old fashioned and overrated, if not totally unrealistic. Someone who could help you weigh the true significance of this relatively minor "tragedy". As one poster said: most guys had sex before marriage (whether they should have, were suppose to or admit to it .. most did). Most enjoyed it; that's very "normal". It might make them better lovers with you and it could even make them appreciate love making with you even more (by having some comparison and not just being curious what it might be like with others). A counselor could help you OBJECTIVELY sort out what things are REALLY important to you and in a marriage and help you see how well (or poorly) he measures up to other more significant criteria. I could elaborate, but won't here. Spend a few sessions with a professional counselor (sex therapist, marriage and family counselor, ideally, or any psychologist as this is not a particularly complex issue to any psychologist).
The counselor will help you to see how self defeating your thinking and feelings are presently; you see how bad it is for you (and probably for him too). Then they can help you work on your "perspective" on this ... to take it apart, analize it and reconstruct it so it makes more sense to you and so you can probably let it go and move on (or alterantively will be unable to and then probably will be told you should end the marriage). I think it can be resolved if you are at all open minded and wanting to get it resolved and to MORE FORWARD in your marriage.
The other approach if you are unwilling/unable to get the counseling would be to TALK IT OUT with him. But that's tricky. You have to BOTH approach this self help method with the right approach. Maybe you could try "role playing" where he acts out how upset he is and why it hurts him (your part) and you could act out his part (how it did not mean anything really to him and he is just sorry you found the silly tape and that it hurt you and how much he really does love you). Sometimes this is very effect ... better than each arguing their own side of it .. as it can make each see the other's side and feelings better even when just role playing ... as opposed to fighting it out with arguments telling the other WHY YOU ARE/WERE WRONG. Only a very mature, calm couple can really do this self help type stuff effectively. Maybe you can; maybe you can't. If you can't, then you only have outside counseling to help you resolve it ... as they will NOT argue with you, nor will they perceive it all just as you do; they will be objective.
Lastly, I can tell you that who he had a little fling with before marriage will someday seem very insignificant to you, after you grow older together, have children and are there for each other over the years during stress, health issues, child raising and all. It will some day seem almost silly ... compared to the bigger things that will come up and become part of your marriage. For that reason, if he is a good man and you love him and think he loves you, I would think it would be best for you to put this matter behind you, out of mind, talked out and resolved and get back to loving him and having a happy marriage again.
Hope this might help you. I might add, I have been in your exact position and I wish someone had given me the above advice; it would have saved me a lot of heartache and a divorce from the first wife.
ROB