Screaming at night now

My LO has always been an amazing little sleeper. He usually sleeps right through the night. He was going to bed at 9pm, but he gets sleepy now around 8pm. He usually wakes up around 7:30am and nothing in the middle. Well...he was waking up screaming in a panic that had me so worried. It seemed to be on days when he saw his daddy (that's a long story). That has seemed to phase out a bit, but now he'll wake up at night screaming. I'll go check on him, comfort him and kiss him goodnight. He calms down quickly, but the second I go to leave the room...game over. As long as I'm in the room he is fine, but if I leave the room or even head towards the door he screams. I tried to let him cry it out but he just gets more and more upset. I mean the kid can scream bloody murder. He throws his lovey out of the crib and we all know there is no sleeping without the lovey. I'll go back in...comfort him, give him a blanket, offer him milk....nothing. I have to sleep in the chair in his room until he falls asleep. Then tiptoe out of the room hoping the squeaking of the floor doesn't wake him up and pray that those little eyes stay shut. SO frustrating! What the heck is going on? He is almost 18 months. 

Some thoughts: 

 - LO and I moved out into our own place in April. He has supervised visitation with his daddy right now maybe three times a week. Maybe something is upsetting him with the situation? Everyone is getting along quite nicely given the circumstances.

- He has stayed the night at my parents place maybe six-seven times. He sleeps over there in a pack in play in my mom's room.  He is getting spoiled having someone in the room with him when he sleeps?

- Are we teething?

- Are we cold?

- Just tell mommy and I'll fix it!  

Any other thoughts, ideas or suggestions? He sleeps with a fan on and no light.