'Best friends' keeping secrets ...?

I have these two best friends and I found out in Science today that they'd been keeping a secret when I heard them whispering and saying don't tell ____ (blank for my name.) I said in a jokey way, "Please tell me ... it's not like I'm going to tell the whole school and the headteacher!" Then my friend (let's call her A) said "Hmm, well you might tell B." (My other best friend who is at a different school and I have known since I was a baby.) I asked her what was she talking about and she said that I'm always telling B things about her and C (the other best friend who she's sharing the secret with.) I asked her how since she doesn't have any contact with B (B doesn't social network or use the computer a lot so she doesn't have email too) and she doesn't even like B either. I also said that I would never do that since I wasn't that kind of person - and I'm not I wouldn't even dream of doing that!- and I asked for some proof. She replied by just saying "Whatever I don't care." So I ignored her and went to my seat then later she started talking to me again like nothing had happened then after I turned my back on her she asked me why I was going in a mood. I told her that her and C are sharing secrets behind my back even though were all supposed to be "best friends" and that they don't trust me for a reason that's obviously made up. She said that she was just joking and that I need to take a joke, but she still couldn't tell me because her and C want to keep it between them because it was something about a boy. I just told her that it was a rubbish excuse and that as friends we were finished because they are always keeping secrets and leaving me out, so I ignored both her and C. At lunch her and C had the nerve to ask me why I was ignoring them then when I answered they just said that I was being moody. I walked away and carried on ignoring them for the afternoon then one of my friends (D) said that she hadn't known me, A and C were arguing so she went outside with them and they told her about it and that C had said "If she goes on like this anymore I'm gonna smack her out!" Which actually upset me because even though we aren't friends anymore as a rule you don't really bring violence into it! I have now deleted and blocked them from Facebook and I have another circle of friends which some of them are best friends but I don't speak to them as much really. I could hang out with them and stuff but one is in a different form which is the one who's like one of my best friends and I get the feeling that it won't really work out hanging out with them all of the time. Just a little bit more on A & C, for me I felt this argument was the last straw because they are always kind of ganging up on me & going off and linking arms and I'm just stood behind them feeling left out. They never call on me to play out or invite me anywhere and C thinks it's the most hilarious thing to sware in all of her friends face and insult them but then laugh about it. (She does it to loads of people and thinks it's really funny.) They will turn their heads away from me and whisper about things and once when I was near the balcony on the top floor of school C jumped up behind me and pushed my back! But anyway, do you think I was being moody or I was wrong here, because I think I might be right but your opinion? Should I make friends with them again or should I just ignore them? What should I do about these friends because it's really getting me down and there has been so many times where this has happened and they gang up on me then if I don't make friends with them again they always hang out with my other circle and try and take them away from me. Please give advice I'm honestly stuck on this one, sorry it's so long!