S.B.
I just went through a similiar thing with my now 4 yr old when he was 3. He started getting his night fears and thats why he wouldnt sleep by himself. He thought there were monsters and some nights he thought we were all gonna leave in the middle of the night without him, not sure why.
We dealt with him in our bedroom for almost a year till he turned 4. We got him out of our room by using the Big Boy talk. He got a brand new bed and CARS bedding for his birthday but the deal was if he wanted big boy stuff he needed to sleep in his room like a big boy. It worked for us. Good Luck!