DS is nearly 4. He's always been a bad sleeper (resorted to co-sleeping until 2 as he woke so often, at 2.5 had to do the "back to bed" technique to get him to go to sleep without being hugged, until recently he'd get up every night and get into bed with me or exW).
Out of the blue in the last couple of weeks he's suddenly developed an intense fear of monsters in his room, so he cries about not being in there without someone else. He's also insistent on checking all doors are locked in case someone breaks in. At my house, he will not go to sleep in his bed, he just follows me back downstairs. At exWs he expresses the fears but ultimately goes to sleep.
I've tried talking to him about his fears, explaining monsters aren't real, explaining mummy will protect him, buying a new "magic light" to keep monsters away, bribery, threatening (and going through with) taking away a treat the next day, lying down with him (he says he knows I won't stay because I'll go and eat my dinner).
I'm at a loss, what can I do? I don't want to be mean to him if he's genuinely scared but at the same time I need him to go to be able to sleep without me!