Indulge me MN-ers. I personally got the 'I've not been happy for some time' line and it turned out to mean 'I've met someone else'. Mealy-mouthed variations would be 'I don't know what I want any more', 'I've never really loved you', 'I'm not sure if I still love you'.
So have you had one of these lines and did it eventually turn out to be an OW/OM?