I would leave my friends and play with the new kid.  But If the new kid is mean I would go play with someone else.  Have you ever been the new kid?  Have your friends ever not wanted to play with the new kid and you are the only one?  Did you ever not want to play with the new kid?  (I hope not for that last one).  Being a new kid is sometimes hard.  give them a chance to get to know you.