My nana’s boyfriend 😕 PLEASE HELP

My nana has been with her boyfriend for 3 years, and this year, he’s been acting weird. At first he’d just stare at me a lot, and give me money. Af first the money was 10-20 and now it’s 50 every time he sees me.. my nana and her boyfriend lives directly across the street from me and my parents. He always makes up excuses to be alone with me and he told me he loved me and can’t stop thinking about me.. I want to tell my mom but I’m scared she won’t believe me.

I’m only 14 and I KNOW that it’s WRONG. My nana has been batting dance for a year now and she’s starting tint to be her old self again. I know it would crush her if she found out.. I’m always uncomfortable around him and he always asks for hugs.. 💔 I literally cried in the car when me, him, my mom, and my siblings, and my nana were coming back from a festival because I was thinking on how I could tell her. PLEASE GIVE ME ADVICE!