What can i do my boyfriend just broke up with me? help!!!?

i am 20 and he is 22. we been together for 3 years since high school. we are so happy and then he just do this out of nowhere by texing me. we always have this problem because he gets scare of a new begginig with me. now this time he told me that he has been looking at girls and dont want to cheat on me. and he said that he dont want to get married or have kid. i am hurt so much i dont know what to do i need help i cant stop crying i love so much. never told him i wanted that but he just dont want to heard me or even talk to me. i dont what i did wrong? i want him back but when i call him he talks to me with so much hate and says to me that is over and then hang up on me. what should i do? please some one help!!!!