Messages in his phone

You know as women we have that intuition that tells us when something isn't right in our relationship. well to give a little background me and my boyfriend have been on and off for over 5 years. this last time. we have been going for almost 2 years. my daughter calls him daddy. he's been around for her like she were his own. well that institution kicked in and kept me up all night. finally (i know i was at fault in this) i look in his phone this morning. low and behold the set of texts directly under mine are this woman. i look at a few texts back and forth him calling her babe. texting when he wakes up. his sending sexually suggestive comments and her responding "all i want is you!" i do not know how far this goes. i couldn't stomach seeing it all. could just be "sexting" or someone to talk to. but that's what I'm for right? we have been trying to convince for almost a year now. i defiantly do not want to bring another child into a broken home. and i guess i am just at a loss of what to do at this point. and didn't have anyone to talk and get advice from that wouldn't be partial to either side. help. i need some insight.