Messages do pop up (Skype or FB and even e-mails) which you can read as they scroll up the screen - if you are using someone else's pc it's difficult to avoid reading them. That said I agree that really at 19 her sex life is her own affair and you shouldn't interfere. Her boyfriend could indeed have been joking or may be part of an earlier conversation taken out of context so best not to let on that you've seen his message.
It had to come; Farage bringing ICE advisor to UK



