Hi fellow students, I'm sure many of you have some awkward step-parent experiences. I am currently having one of those myself, and I was wondering if anyone could help me figure it out: When I was six years old, there was a Monster who lived under my bed, in my closet, and on the ceiling. I was so scared of it that I kept my dad up all night asking him to get rid of the Monster (which was not very nice to the Monster, but I was six and had never seen a Monster before). The Monster started bothering all of us, so my older brother used the famous Power of Love technique, which seemed to get it out of the house. Recently though, the Monster is back (probably due to the Ten Year Rule) but it doesn't seem interested in scaring me. It has even started Appearing in the daytime. Here is the part I need help with: ever since it came back a few months ago, it and my dad have been become friends(?) and started to more and more things together. It has even started having dinner with us. Yesterday, when I came home from school, I saw them watching a romcom together. Please help?

Tldr; How do I tell my dad that I'm uncomfortable with him dating the Monster who used to live under my bed without sounding like a total jerk?