Help needed

I'm 15, 16 in June and I need some serious help. (Warning this may be quite long) i have been with my first proper boyfriend for now 7 months, before I was with him I had made some bad decisions in life and got a reputation but I regret it. I used to get a lot off attention and I will admit I loved it, before me and boyfriend got together I had been seeing someone who I had gone out with when I was quite young (13) so I don't count it but that ended badly and then I met someone else who told me everything I wanted to hear and stuck around unfortunately he wasn't as good as I thought and he had to go to prison for ABH I think and I was so upset because even know we wasn't really like that I missed him his calls and his texts, when he got out of prison I just started going out with my current boyfriend and he texted me saying "yo baby I know you have a boyfriend but I don't care I will knock him out" this clearly upset me and we would argue and he argued with my boyfriend. He then started asking questions and I told him we had broke up but it was my fault which I would agree it was im not easy at times. And he would say comments like he makes you think it's mostly you but I told him straight it was over between us because I was happy and he after coming out of prison still didn't wake up and stop doing the stuff that put him in there the first place so every known then I get the odd text sometimes I reply or sometimes Ignore it. So at the end of last year I stopped wanting to have sex with my boyfriend and I'm not sure why, before I was always wanting to have sex and he thinks it's him to be honest I'm not sure what it is it but it don't bother me at all, but now I'm horny all the time but not for him I look at boys and imagine things and I don't even mean to, also during our early months of our relationship I got accused by everyone at school I was cheating on him with another boy who had dmed me on Instagram saying he liked me, once again I was getting attention and I loved it and the boy is good looking but I blew him of and told him straight no. But recently I miss the boy who was in prison I read over the chats and I miss him and now the other boy from Instagram I keep thinking about sleeping with him... I don't know what's wrong but someone help!