Thank you @Isitreallyme177**@SpringlikeBunk and @Stayingstrongish for your viewpoints, I really appreciate them.
I think you've hit the nail on the head @SpringlikeBunk - even if 10 people commented and unanimously told me I was overreacting and living with an ex was nothing for me to worry about, the fact is that is does bother me and maybe I should listen to those feelings.
As a worst case scenario - they're still together, I'm being taken for a mug, and I'm inadvertently becoming the 'other woman' . At best - he's telling the truth, they have indeed split up, but I'm twisting myself up into a ball of anxiety because I'm not comfortable with the situation. Neither are brilliant, are they?!
It's just annoying as he's the first guy I've actually been excited about for a long while. There's always something!
I think my best bet is to keep in touch, keep on each others radar, but maybe scale back the meets/contact until his situation changes (which he's assured me will be very early next year). Watch this space!
Also, it must be the time of year with Christmas approaching, but I've got previous irons/fwbs crawling out of the woodwork on a seemingly daily basis so maybe a couple of 'meetings' there could help bring me down to earth...