I know I'm late to this post but I think you need to tell him you found them in the same way you told us. He needs to come clean about it. If he has nothing to hide, then he shouldn't be angry that you found them. If you are going to be husband and wife, you shouldn't be keeping anything at all from each other. If he gets angry at you, I would be suspicious. But from what you have said so far, I don't think he will get angry. Chances are she does love him and maybe he feels guilty because he does not love her back romantically but cares about her very much. Even if this is the case, do you have something to worry about? If she does love him but he does not love her, you have already won this battle. So, I'd try not to be too jealous.