Mom cheating on dad

Hey girls. I'm 18 soon to be 19 I have recently suspected my mom of cheating on my dad. It started with me seeing her phone light up and I read "I love u too" from this other guy. I couldn't read anymore than that she said "I love u" first because I felt like I was invading her privacy. I hoped it would go away because we lived like 12 hours away from him but now we have moved and we live 2 hours from him. He came over to help us move and they kept disappearing and I couldn't go looking for him in fear that my suspicion would be confirmed.  Even today he went with her to her class reunion even though he graduated the year before her. He has a wife and children too. I'm no saint and I have cheated on my own boyfriend but it wasn't an affair. It was a laps in judgement and I have delt with it. I don't know how to deal with this. My mom has no idea I know. My dad for as far as I can tell has no idea and there is no way I would ever tell him. That's not really my place. I don't even know if my 16 year old sister knows. It just makes me sick and I don't know what to do. Do I just keep acting like everything is ok or do I confront my mom?  Because I cheated does that mean that i don't have the right to confront her?  Can anyone help?  I don't know what to do.