I’ve just been through the exact same thing! Broke up but we have a joint tenancy so still have to live together!
Rang UC as we had a joint claim. Started a single claim no problem! Just make it clear you’re living in the same house BUT you’re not in a relationship and live as 2 separate people. You share time in the front room, cook meals separately and in separate bedrooms.
I claim child benefit for all 5 children so I claim the child allowance on UC. Half the rent cost and my single person allowance.
He set up a single claim. Single person allowance and housing allowance for half the rent.
Don’t let them tell you it’s not allowed or possible! I spoke to 3 different UC advisors on the phone when making my changes and got different advice each time! Lucky I got more opinions because they gave me the wrong advice initially and I would have been underpaid £300! And the payment wouldn’t have been paid on time if at all.