How to get rid of a guy politely?

I met this boy about 5 months ago (he's friend of friend of friends or something like that). he asked for my instagram and I didnt see why to deny.

since November he started replying and liking every story I post, and he waits for me to get online so he can text me immediately (he admited it himself). he's also tryed creep corny chats.

I don't want to be rude and simply block him cuz there's a chance we eventually meet again. pls help