Saying No.

There’s this guy that sent me a message on Facebook and I replied. Since I have zero friends and only have my boyfriend of four years I decided to reply to him, and be friendly no flirting I wanted to be friends with him because it’s rare for me to get a message on my social media’s. We didn’t talk consistently and recently right now he said he’s really into me and that it he plans on asking me to be his girlfriend once we see each other next month which is true we are from the same little village in Mexico and I don’t know how to say to him no that I was just being nice because I wanted to be friends nothing more. To be honest he seems like a really nice person and that’s why I’m having some trouble what would you recommend?