How to nicely reject this guy?

[Valkyrie]

Honestly, some people won't get the message unless you flat out tell them 'no', as much as you don't want to, you have to be blunt or he'll be led to believe he has a chance. Say that you only see him as a friend, and nothing can change that. He can't get out of the friend zone that way, and worse comes to worst - say you see him as a family member, so there could never be anything between you. Next time, just make sure you know the person well enough before you give your number don't feel obligated to be nice, it can backfire because I've tried being like you and some people just don't get the hint.