Hi there!
I can totally relate, having OCD (which for me, includes tons of intrusive thoughts), I have experienced many unwanted thoughts/obsessions about celebrity figures. It can be quite debilitating if the thoughts occupy the mind to a point where real life isn't being lived. Personally, I often go into my own thoughts to escape the negative aspects of the real world...not sure if that's one of the reasons you do it.
For you, are the thoughts created, intrusive, or both? (For me, it's both). If they're created, then it will be easier for you to stop the thoughts than if they were intrusive.
I still struggle with obsessions in general, and something that helps me is trying to do things in real life that give me pleasure, and usually I'll feel as if my time spent in real life was much more fun than time spent in my own mind. Do you have any hobbies that you enjoy? Exercise? Art? Sports? Anything works.
But also know that any obsession is hard to quit. So if you end up obsessing about this celebrity figure and feel guilty about it, try to forgive yourself and move on. It's ok to be a little obsessive about a celebrity, but your life is more important than theirs.