well the monster can be tamed, but it is going to require some work on both you and he's part. It might help if you take the full size bed down and put up a toddler or twin bed, that way there is not room for you, and he might understand that. But if this is just his big boy bed, then he will need to get used to sleeping by himself. It is not that he needs you to be with him, it is that he has gotten used to you being there, and the comfort that brings him, and he is going to pitch a fit when you try to shake things up. you need to do it slowly and start by only laying with him for a few minutes maybe 10, and then shorten that each night by a couple minutes and take about a week to actually get to where you don't lay with him when he goes to bed, then sit beside the bed and maybe hold his hand or something but only for a couple of minutes, then work your way out the door. Use a chair and actually move it closer to the door each night until you are sitting outside the door for a couple minutes, This whole process may take 2-3 weeks, but if done gradually it will give him more time to get used to it knowing that you are still near by. Leaving them to cry themselves to sleep is great when they are fairly new born, but he has just developed a habit and you will have to break that habit. Good luck.