what the fuck are you doin in your mum's phone man? it's not your place to find that shit out, dude, any way you handle this is gonna end up fucked up. i wouldn't tell anyone shit, but the ONLY person you have ANY right to talk to about this is your mum and your dad, don't bring anyone else in on it unless your sister's old enough to deal with it (ie. 20+). that said, assuming it's not your dad's new phone number she's texting to, good luck man, that would be my worst nightmare to find. but then again, i'd never find it, because i don't touch my parent's phones just like i expect them not to touch mine. what if you were cheating on your gf and your mum came in and was like, "mate, i saw all those dirty messages you sent to that girl that's not your girlfriend. im telling everyone." how the fuck would you react? not well, that's for sure. handle this shit with care man, much care. this is a fragile situation. or a huge misunderstanding.
Instead lets ensure that his family gets torn apart beyond repair. OP, your mom fucked up. People make mistakes but do what you feel like you have to. Just be wary of the consquences because they will be life altering. Your life will never be the same.
i think he should talk to his mom about it all.... I mean its really no different than her cheating on his dad. I mean what if it wasn't over the phone and she brought this guy over? Then should he still mind his own bussiness, knowin his mom is gettin pounded upstairs while his dad is at work.... no he shud prolly talk to her about it. I do agree that he shouldn't go thru her phone, but he did... and thats done now. He shouldn't havta live with the fact that he knew his mom was cheating and his dad has know clue, what if it goes on for a year or something. If she knows that her son knows than it will most likely stop. I don't know tho, just my opinion.