@teebee85: While I agree with the others that the correspondence is harmless and very infrequent, I have a different concern.
I was with someone for three years who saw any communication with an ex — ANY communication, in ANY way, about ANY topic, and even if I’d only ever just had feelings for that other person way, way in the past — as a violation and disrespectful of our relationship. He would be livid.
Hell, he was livid. I didn’t understand it at the time, but one of the biggest reasons we didn’t work out was because we viewed relationship dynamics very differently. He was wildly jealous any time I so much as mentioned any male colleagues at work, but if I avoided mentioning them or said “my coworker” instead of “him”, that was just as much of a neon sign to him that I was talking about a male. And, clearly, if I was talking about a guy then I obviously felt an attraction to him, because why else would it stick in my brain to remember for later? I was young. I was naive. I did not understand that this was jealousy and a need to control the situation. I tried really hard to feel the way he felt about it. But I didn’t, and I couldn’t make myself. So I would, on occasion, send a harmless email to people who found me on Facebook. When he found out, he went crazy. But then he went and did the same thing to me. I didn’t have a problem with him contacting exes. But I had a problem with the notion that he found it disrespectful but did it anyway, thus disrespecting me, based on his own rules.
To bring this back around to your situation, if your fiancé would have a problem with you contacting an ex (any and / or all exes), but then he does the very same, it says to me that he doesn’t have the same respect for you that he asks of you. This is the only way I see this as a problem. I have a very hard time dealing with double standards in relationships. In all things, but especially in a relationship that is meant to be equal, and mutually respectful.
If the texts and the act of texting truly don’t bother you, I wouldn’t bring it up. In fact, it’s a very difficult situation to approach, anyway. You either mention that you were looking through his phone, which is rude, or you try to bring it up in a roundabout way and catch him in a lie (or hope he tells the truth), which is sneaky in a bad way. If your relationship is one where you can be direct, I would go for it.
Note: I didn’t tell that story to try to work you up. I told it only to explain why I would see it that way. It is entirely possible, and even likely, that you guys don’t have “rules” about exes.