Your missing the point.

It's not about whether she's seeing other guys while she thinks she's in a relationship and is therefore no good as a gf but still perfectly operational as a fb.

The problem lies in the fact that 'big bad whatever the feck your name is' has now flipped from seeing her as a needy little tag along to becoming the needy little tag along, because shes fucking around with his head.

THATS why he has to blow her off and move on. Obviously as it's got to this stage now, it's passed the point of no return. Once you get feelings for a girl, it's either GirlFriend or GetFucked.