HELP! i got myself into this mess but i need help getting out?

ok.....since 3rd grade i had a huge crush on this boy. now this present time......i asked him to be my boyfriend and he said yes because he liked me too and we both knew we liked eachother. he is NOT mature at all. its like hes still 10! when im on teh phone with him i hear him yelling at his 7 year ol sister who was just asking him to ask about my cat (i named my cat pizza and she thinks its funny so she always lieks to ask about him) i keep thinking i liek him....and then dont like him......break ups were soooo much easier when i was ten :( i do NOT like him anymore because if he causes my mind this much trouble just imagine what would happen if we were *gulp* MARRIED! help help help how do you break up with a very sensitive, imature guy. not to mention im afraid that his mom wont liek me if i mess with him too much (when i say mess with him, i mean his mind so dont think what i KNOW you ar ethinking) she told me that i make his day when i call him (he never calls me) and shes really nice, i dont want her to hate me. also him and i have a mutual friend and i dont want her to hate me too. please help.how do i break up with him without his mom hating me and hurting his feelings?