I discovered my mom’s affair, what now?

In July, I discovered my mom’s affair after going through some of her text messages with her best friend. The I texts I found were vulgar descriptions of sex with an unnamed man. I knew instantly that this was not with my father. The man was later referred to with an initial, so we figured out who it was. My sibling and I (both college aged) had a theory that something was going on because she was being more secretive about her phone, and constantly texting. When we’d look at her screen, she’d close the app she was in. My sibling and I both worked full time over the summer and now attend out of state universities so we haven’t been able to gather more evidence but we’re 99.9% sure it’s happening. I’ve glanced over and caught her texting him, but she always closes the chat before I can read anything. I just feel sick that she can cover this up and be so deceitful. I knew she and my dad didn’t love each other, but I feel bad that this is all behind my dad’s back. Ideally I’d like to catch her in a lie or find some way to expose the cheating where she doesn’t know that I’ve gone through her phone. She’s turned off her location sharing with everyone, so that’s not an option. Any suggestions? And any advice on how to move forward? I don’t want to blow up my family, but my sibling and I can’t look at her the same knowing that she’s an adulterous liar. My dad doesn’t deserve this, she’s leeching off him.