I found out my mom is having an affair. Should I tell my dad?

Question: “Eight years ago, when I was a freshman in high school, I found out my mother had been having an affair. Over time I was able to determine that this person is an ex-boyfriend of hers. They talk every day and I have gone through texts that allude to both emotional love and physical intimacy. He lives super far away and my mom doesn’t travel, so I’m positive they don’t physically see each other. My mother also talks about us to him, and often sends pictures of us. 

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