My best friend is a compulsive liar...I think?

Well I'm a 14 year old girl I live in England. My best friend is a guy of also 14 (yes just a friend nothing more and he has told us he is bisexual although I think he's just gay :P), let's call him B. Anyway I've known him for 4 years since I started school with him in year 7, when we were both 11. H has lied to me since I first met him about his whole life.

A few weeks ago I found this out for sure by confronting him about it on Facebook email. I wasn't going to because I have read many sites on it and they all said confronting didn't help. But I had to we're so close but recently the lies having been getting more and more serious and relevant.

When I first met him in year 7 he told me many lies, that he was adopted, that he had cancer and was going to die (later in year 8 he told me he was cured), that he lived in Japan until he was 5.... etc. Anyway he confessed to all these lies (other than the cancer one) he promised that he would never lie again, I gave him another chance because he's my bff and I love him (as a friend). He told me and my friends a couple of months ago that he was Bipolar. About a week after he confessed to my friend that it was also a lie. At this point I got really mad at him as even after admitting to his earlier lies he had denied that lie. He also recently told me and a couple of our really close friends that he tried to kill himself by taking too many drugs (happy pills WTF? you can't overdose on happy pills?) Anyway B told me that he got them off this guy he met online, let's call him G. They guy had Facebook so I added him as a friend. He was really nice, 16 year old gay guy (definitely not a pedo) and I talked to him on chat. He told me he'd never even met B in person and had only talked to him on webcam. I text B asking him where he got the drugs (I had not yet told him I had spoken to G). He said G. So I asked him if he'd actually met him and he said yes. Then he sent me a text saying not the same G though. I knew this was a cover up because he said it's not the same G I had been talking to so clearly he had talked to him since his last text. I talked to G again and asked him if he'd spoken to B. G said yes he had texted him saying it was another G. Yeah this is getting confusing :s Anyway B told my friend that I had ruined the only good thing in his like G. But G told me that he was barely in his life and he already had a boyfriend, plus they had never met. B has told us he's depressed and keeps making up diseases he has. At the moment we aren't talking to each other. He thinks I hate him and he's really mad at me. I am unbelievably pissed at him but I dunno what to do. We've been friends for 4 years and we have all our lessons together. i can't trust anything he says but he's so funny and fun to be around although I dont think I can deal with his lies! Help please! What can I do? :s