Anyone else find themselves daydreaming up a situation based on a small piece of reality?

How do you take back control? Lately it seems like my mind is constantly wandering to places I’d rather it or go. 

I’m fantasizing about a close friend. Both sexually and romantically. I don’t even know that I truly have feelings for them. I kind of think anything I feel is based off this fantasy I’ve tried to escape but I can’t seem to let it go.