friend problems :( Options

[Colour_me_stupid]

Ok so heres the deal
Me and my friend W are bestfriends. and we became with two other people P and C who are also best friends. so we're all really really good friends for about a year and a half. we've all had history with eachother before.( we were friends with one or another at a certain time. we've known eachother for quite a while.)
anyway, so it all started one random day where C would go home for lunch and of course P and C are best friends so they go together and they wouldnt invite me and W. so we shurgged it off, no big deal. but soon after it would get more often. and after school they would ditch us to go to some stupid guys house to smoke. (which is majorly lame, since they told me they would never ever do it)
On my birthday P & C made up some lame excuse that they had to go watch their pets and couldnt come to my little shindig. apparently P was watching her pets, getting her mom a present and waiting for her grandpa to come home. why couldnt C go if P was doing all that stuff?? suspicious. and so i found out they ditched to go smoke pot again.
some friends. the next day at school the guy they smoke pot with was like "wow that was a goood day yesterday *smiling at P & C* *looks at me* ohhh yeah it was good cuz it was your birthday"
they were all like omg , i swear on my moms life i was watching my pets blah blah
i kind of let it go.
then last weekend, me and W went to my other friends house. he put on webcam with P, but she didnt have one but she had a microphone, but she didnt know it was on. so to keep it short, we listened to P & C talking shit about me and W for an hour. they were saying how W was fat and how were so annoying, 2 faced and they dont even really like us that much.
so we were really upset so we confronted them on it. and their excuse was
"I DONT HAVE A MICROPHONE ISWEAR ON MY MOTHERS LIFE" uhhh you obviously have a microphone if i freakin heard you. then they were denying what we heard them say. and we know their lying cuz we heard it ourselves. then 5 minutes later they said "it wasnt directed to us"which makes no sense at all.

so the thing is, i dont know what to do. should me and w still stay friends with them?? everyone is saying not to, but its not that easy. we've had a lot of history. and its hard to avoid them if we see them allll the time, and one of them shares a locker with me. and now they're all acting normal. so what should i do?

[-sincerely]

I'm agreeing with the above 200%. It's hard to stop being friends with somebody, I know, but they sound like the wrong crowd. You obviously know their lying, so .. I mean, honestly, pot?!