It's thought their conflicting work schedules caused problems.
'[Bethan is] a lovely girl with a big heart. But she was hardly seeing David because he's so busy,' a friend tells the News Of The World.
'She became fed up of spending her nights alone and couldn't see a future together.'
David, 36, met Bethan, 28, in November. She works as an assistant at BBC Cardiff, where Doctor Who is filmed.