Why does my ex-boyfriend act so strangely in this way?

[Indie Poser ;3]

We've broken up for over a month now and im still in love with him, I'm 15 and he's 16 and he just randomly dumped me for some wild reasons (or rather, excuses). He said he had to break up with me because he "can't" be with me anymore. He also said that it's because we drifted apart due to arguments, because my sex session with him was a turn off, because we're "nothing alike", and even because I "hit on other guys in my school" and because I was attracted to other guys (I just did it to make him feel jealous and love me more though :/) and for "reasons he doesn't want to talk about." but the thing is, it was perfectly fine just a little more than a week before we broke up. He told me how much he loved me and how much everything I say means to him, and then one day he just told me he wouldn't see me or speak to me for 3 months.
After the breakup I tried talking to him with very vague responses. He made a status that I was "trying to get him back" on Facebook and deleted me. He started hating me for no apparent reason!We stopped talking for five days then he added me back and started talking to me again and he said "It's stupid we're not even friends anymore =P" but then a few days later bam starts hating on me like I'm his mortal enemy again. I gave up on speaking to him and then I put up a picture of myself captioned "Dimples" and he messaged me to mock me and said "I don't even see any dimples :')" just randomly! I eventually started talking to him and then he was really upset (he told me a few times before he's depressed) and he told me about his personal problems and how much he hates his life (when we were together he told me he tried hurting himself before - I won't give reasons, he told me not to tell anyone and it still applies now because I love him). So I consoled him, and a few days later I gave him some compliments and he was telling me "Aww that's so sweet" and called me sweet, but then the next day he just suddenly told me not to compliment him again. Then he stopped using his devices, he's never online, and I haven't ever seen him. He only goes on Facebook and Twitter very occasionally, possibly grounded as usual, but when I put a status about people not flirting with other people if they're in a relationship, he just suddenly started hating me again and commented, "lmfao you pretty described what you did to me." why does he act like this? Sometimes he's nice, and then he acts bipolar and starts hating me for no reason...? He is depressed though because of home, maybe he's just emotional?

[Amy]

oh god, honestly. He sounds crazy but I been through it ! So when I was 15 my ex left me also. He wanted my attention, so I didn't give him any. I wouldn't hit him up or talk to him at all in till he would talk to me first. I act like I didn't care, never posted any status or anything about him. I went out with my friends had a lot of friends and act as if I didn't miss or need him. ( though deep down inside I missed him like crazy ) Of course he would get jealous that I was having fun and happy without him and he would come back to me like crazy. I kept in touch with my ex cause he would always text me first (planned worked) and he would act mean to me one day and nice to me the other. So when he acts mean to me, I just ignore him or just be like well.....ok talk to you later. It gets it across you aren't playing games with him.