There is a woman at my DHs work who is 26 (not really relevant I suppose), single. He is 36 (again, not really relevant). She messages him a lot. To me, the messages read as flirty. Stuff like 'miss you man', 'you are my best friend, can't wait till you are back so we can go for lunch'. Sent on his days off. I mostly turn a blind eye. However, she sends selfies of herself to him. Supposedly for him to pass on to his single friend as he is trying to set them up. (This sounds believable but it is kind of a long standing joke- it has been going on 2 years and they haven't swapped numbers or made any attempt to meet).
I suppose what I am asking is, am I being controlling being annoyed about the selfies and the messages. I am confident nothing physical at all is going on but the messages annoy me. If she sends messages like that when he is at home, how are they together at work?