When an 8ft hairy black monster begins following him around and disrupting his life, a lonely divorcee must find a way to get rid of it before it controls his entire existence.
Is this a part of his imagination or a real monster?
If the former, then the conflict is inner if the latter then the conflict is external.
If it’s an inner conflict, you would need to describe the event that made him need to face his inner problems. Was it the divorce? Was it something he or his ex-wife did?
If the monster is real, then the monster’s appearance is the inciting event, which makes getting rid of it the goal. How did the monster come into being and find him? Was it a camping trip? A magical appearance out of thin air? Either way, whatever force or event brought the monster into his life, needs to be described in the logline.
What are the stakes? I only ask because I am not sure what you mean by, “Controls his entire existence” Does this mean the monster is going to mind control the lead character and take over his body?
In other words, what will the lead character lose if he does not get rid of the monster?
However, besides that, I think this logline is pretty close and has a great hook.