Yeah-definitely not splitting. Has its mouth ever been gaping? (the mouth in the picture is not too bad). See how this progresses, hopefully it gets better, but this could be the beginning of a bacterial infection. Don't worry - its treatable.
On the other hand, anemones will also move around when there are unsuitable water conditions. maybe try doing a water change. I doubt it is a bacterial infection (it was doing good for 4 months, right?).