getting over someone? kind of long

ok sorry this is so long but its a pretty long story.

well anyways, this boy named alex started going to my school in 8th grade. i’m in 10th grade now. at first i didnt really talk to him but then a girl im kind of friends with started going out with him from the end of 8th grade to the middle of 9th grade. by then me and alex were friends because he was always with my other friend. in 9th grade we were in a class together and i started liking him but i never said anything because of my friend that went out with him. i felt really bad about it. so then 9th grade ended, and alex told me he liked me and he asked me out. i said no because i didnt want my friend to be mad. i really really liked him though and we still hung out as friends. all summer he kept trying to get me to go out with him because i told him i liked him alot but i didnt want anyone to be mad at me. by the beginning of september i finally decided to go out with him. i told my friend and we talked about it. she said she was fine with it, but that he lies and cheats and she didnt want him to hurt me the way he hurt her. i told alex about it and he said that was his past and hes not like that anymore. so we were going out for almost a month. everything was going perfect, at least he acted like it was. and we always had fun together and we could talk for hours and he treated me really good and bought me stuff. we talked about our past relationships and i found out that he used to sleep around and he went out with ALOT of girls. that scared me because i always go for the wrong guys, and they screw me over in the end. he said he wasn’t like that anymore. it was stupid but i believed him. so everything was going perfect. then last week he broke up with me and said he didnt think it was gonna work out because he just liked me as a friend and he was confused, which makes no sense because even my friend went through my texts and couldnt understand what happened. up til the last day we were going out, all my texts from him were like i love you so much, your the most beautiful girl in the world, im so happy im going out with you, i didnt want to leave your house i wanted to stay with you forever, and then he did the complete opposite and texted me that he wanted to break up. i said fine and he said he still wanted to be friends. i said ok and that it was fine, but i was crying for days. of course he didnt know that though. a few days later i found out from a friend that he was talking to this girl online and he wanted to meet up with her while we were still going out. he doesn’t know that i know about that. it hurt me so much because i liked him for so long and i thought that he had to at least like me a little, since he tried so hard to go out with me. do you think it was just a game for him? i heard that he was telling people he could get any girl he wanted. he still talks to me in the hallway and i have no idea if i should ignore him or say hi and act like i don’t care. i miss him so much but then i think about it and i hate him for what he did to me, even though he said he wouldnt. what do i do? we were so close before and i hate that we ruined our friendship. and i feel so pathetic because every time i get a text message i still hope its him. do i talk to him or leave it alone? and how do i get over him if i still have to see him in the hallways every day?