What do i do if i think my dad is cheating on my mom?

alright, so we were in the car for an eight hour drive, and my mom was driving, and my dad was on his blackberry. i was reading, and i glanced at his blackberry and saw the word 'beautiful'. so i tried to maneuver so i could get a closer look without attracting attention. what it read was, my beautiful princess, i am enroute to new york and am missing you 'something terrible'. then it went on for a paragraph i couldn't read. at the end, it said - i wish you were here, you have all my love, and then my dad's name. he scrolled down a bit, and he was writing in response to an email from a woman. let's say her name was lily walsh. i did actually see the name, i just don't want to put it on here. and her first words in her email were, hello sunshine! i looked up the woman's name on google, and she works in the same branch of the government that my dad works in. she lives in alberta, whereas we live in ontario, but my dad takes business trips out there all the time. i dont know what to do, should i ask him about it? im a lot closer to my dad than my mom, and we have money issues right now as it is, and if something really is wrong and my family splits up, i have no idea what will happen. i dont want to just accuse my dad of this either, in case im way off and its something different, but i cant imagine who he'd be sending such a message to. and yes, i am absolutely positive that's what the email said.