Okay, I will chime in as I have been with my wife 25 years and I can tell you I would be hurt and mad and jealous and everything else that you are going through.
The secret here is if you want to stay married, then you need to play it cool and watch everything. Do not start accusing her or asking a ton of questions every time she walks out the door. Don't whatever you do, keep brining this up even in a joking matter such as "Well, at least I don't have boyfriends texting me al hours of the night." Ha ha.. if you get to that point, it is over, you might as well just end it. Start watching her behavior. As others have pointed out, watch dressing habits, watch her CC accounts. If this is something that is on-going, then she has gone to other means of communicating--so watch her laptop. If you notice cookies and browsing history deleted everyday, then you have problems, but more than likely if she is communicating in other ways, she will slip up and leave a trail.
Or this could have honestly been a mistake on her part and she befriended a guy and it went a little further (word wise) and now she is regretful and your marriage can move forward. Plus the fringe benefits you are getting now are very nice!!
Play this cool for your kid's sake because maybe nothing happened beyond a few texts. But keep your guard up and watch for anything out of the ordinary. Like I said, I have been with my wife 25 years. it would take more than this for me to toss my marriage out the window--but then again my kids are 10 and 15.