THIS GUY IS MAKING ME BALLISTIC!?

Right so I've known this guy for 4 years, Hes a year younger than me and he just won't stop begging me? So basically, This guy used to get bullied way back when i met him and he has literally NO friends so i went and made friends with him (Long time ago) , We're next door neighbours but this guy has some serious issues. He always has a problem with my friends but he always starts it with talking behind their back and he cannot bear me to be friends with anyone else other than him, He is constantly begging me to go out and walk around with him, He just won't stop ringing my phone constantly or knocking on my door and it is hard sometimes to say no to him but he is just the worst beg i have ever met without doubt. Advice please on what to do?