I had a similar problem with my son (now 19!!). He would only go to sleep if I held him and the moment I moved he woke up!
I ended up doing what dragonfly's suggested, but once he got used to that, I gradually sat further away from him after the story, till eventually he went to sleep on his own. I left his door ajar and the landing on.
Has the bed got any sides or guard rail? Maybe he feels insecure in an 'open space'? Also have there been any other changes to his routine that are causing him to be 'clingy'...new baby, new house, starting playgroup etc?