That actually happened to me once too.
I was holding my phone and showing my missus some stuff. And then a text from a former regular WG that I used to see, sent to the phone that said something like "Hey, I am in London this month. Drop me a text for a meet". My heart almost stopped for a second. Luckily, she didn't put in like a big bunch of kisses and such to make it even more suspicious. The missus asked "Oh who was that?" I was quick witted enough to answer, "That's a client we are chasing for a while. Let me quickly called work and see if it's true that they are in London." So I called my office phone's voicemail, and pretend I was having a conversation with someone at work about this "client" that are visiting London now.
I think I managed to got away with that. Missus certainly never asked me about it. Or maybe she is secretly hiring a PI and I will be killed any minute now, I don't know.