If you know you know
Kirsty had grown suspicious of Kieran's plan - he had visited all of her parents within 3 days, he was being secretive and being territorial of his phone. She asked him and he gaslit her so hard she cried. Two weeks later, during a trip to Orkney - where Kirsty's Nanny and Grandad live - he proposed on her favourite beach, Waulkmill with her grandmothers ring.