My bf of over a year cheated on me?

im taking this alot better than i thought i would but its still hard. My bf of over a year dumps me and tells me he met someone else and slept with her the night before. But the thing is I NEVER imagined he would do this. He was the best bf i have ever had. He was my best friend and always treated me so good so when he lost his job and his car i stuck by him. I did so much for him and this is how he repays me? We had our whole future planned out. I dont even know when or how he met another girl...we were together almost every night. I just cant believe he doesnt even care what he did to me when he was the most caring guy i knew. Its so hard to figure out what was a lie and what wasnt. We always had so much fun together, so many inside jokes, so many dedicated songs.. how can none of that matter to him at all? and the thing is a couple weeks ago i tried to break up with him because i was getting a little sick of our bickering but he begged me to stay! then springs this out of nowhere..and he is acting like the one who got hurt in this.. when i got to his house to pick him up he was mad and just telling me to leave and go away and thats when he broke up with me. Its sad because i want my best friend back but i know i could never trust him again. But i just want him to realize he messed up and beg me back...but what if that doesnt happen? Im trying to keep busy and move on but its hard when your whole life surrounded them. How could he do this? He acted like he loved and cared so much ...everyone was so surprised.