Am I wrong?

I was having dinner with my friends a few nights ago when I spotted my father in law having dinner with another woman in the restaurant. They were holding hands and kissing. I know for a 100% fact that my husband’s parents are not in an open relationship or thruple situation so I knew this was cheating. I immediately took a photo for evidence and then told my husband what I saw when I got home. My husband’s reaction was not what I expected, he basically called me weird for infringing on his dad’s privacy and taking his photo in public. I told my husband that his mom (my mother in law) has the right to know what is going on. My husband told me to not mettle in their business and said it’s not my place. As a woman I know I would want to know if I was being cheated on. I told my husband he has 3 days to tell her and if he doesn’t, I will. Well long story short, he never told his mom so I did. His mom is heartbroken and wants a divorce after 30 years of marriage. Turns out the affair has been going on for almost a year. My husband is furious with me and told me that I betrayed him & his father’s trust and that it’s all my fault that the marriage is falling apart. I told my husband that if he truly feels that way, then we ought to divorce now as well because I will not spend my life with someone who condones this behavior. My husband says he already knew about the affair but said that he’s adult enough to know when to keep his mouth shut and accused me of loving drama. My husband and I have been married for 2 years & I am truly considering divorce over his perspective on this. Am I in the wrong?