Yes, I think you are being unreasonable. Although I agree that it is hurtful and damaging to all concerned for people to have affairs, I don’t think essentially blackmailing the guy with threats about telling his wife or employer is wise. Your issue is with your wife.
You don’t need any corroborating information. Whether or not she is having an affair, your relationship with your wife has broken down and you don’t trust her. That’s more than enough reason to have a frank conversation with her. You don’t need an admission of guilt. You do need to figure out what has happened between you that you even suspect that something is going on.
Blaming, accusing, and threatening is not the way to go into a conversation if you want to save your marriage. Shaming and blaming will only make her defensive. Instead, talk about your hurt and concern. If it’s true, let her know how much she means to you and how you want to retrieve the closeness you once had. Acknowledge that you probably contributed to the situation, even if you didn’t mean to or if you don’t understand how. Suggest that the two of you go to some couple counseling to see what can be done to repair your relationship. Unless she has already made up her mind to leave, that approach could open a new chapter in your marriage.
I wish you well.