After some advice found some messages on my partner's phone which are pretty much chit chat about a hobby him and this other women have.
However one or two of these messages seem to be flirty, maybe testing the waters to see what reaction they get? Also the women has "accidentally" sent a kissing emoji then made several other comments about it "oh look what I've done", "silly me" etc
Can't decide if I'm over reacting to say something now when it could easily be explained away. Or if I should see how it pans out kinda feel like I'm leaving things to progress between them by not saying something now. But also worry he could hide it more in the future if I say something now.
Just to clarify they have not met in real life, we are not local to the women, she doesn't know his name/age/face etc in real life.