This is obviously very upsetting and won't, in your mind, just go away. It may well be that it has struck at the root of any trust you may have in him. If that is the case, there is only one way to deal with it, you need to talk to each other, and you have to reach a position where you are happy in your own mind with the outcome, whether it is walk away or stay together.
Pretending that it is nothing will not do you any good and before long, he will know somethig is wrong with the way you are treating him, so better to get it out in the open now and resolve it one way or the other.