Most Helpful Guy
You know no matter how kind or concerned you are for him. You can't not hurt him, ultimately work your own feelings out first and if you're absolutely sure, take him aside privately and break it to him, don't say stuff like 'its not you, its me'. Admit that lately you haven't been feeling yourself lately and right now the only person you've room for is yourself.
Most Helpful Girl
You should arrange to meet with him and just be honest and open because the longer you wait to tell him the more attached he will become. It's better for his tears to shed now while he isn't that deep into the relationship than when he finally falls for you