DS1 is nearly 7 and in a mixed age class (years 2 and 3, it's a very small school) with people he's mostly been with since Foundation or preschool. However, the social dynamics are tricky for him. His best friend, or the boy he thinks is his bf, seems quite popular - lots of people want to play with him. Sometimes, this child will annexe off the rest of the group of boys who hang together, DS1 included, in a way that excludes DS1. 
DS1 is fairly socially unsophisticated and can't see what's going on, or what he could do about it - it just makes him sad. I've encouraged him to make friends outside this tight little group of 4, to cushion the blow of him being excluded from time to time (and also tried to flag it up with his teacher). Thing is, it's such a small class that there's a very small pool of children to do this with. Then...
a new boy started, around a year ago. He seemed friendly, if a bit manic. DS1 initially bonded with him quite well but recently, the attentions of this other child border on the obsessive. He's completely obsessed with a range of toys that DS1 has and that he, the other child, doesn't have, but he also just wants to be with DS1 - DS1 says, all the time at school.
'New friend' doesn't get on at all with DS1's small group of pre-existing friends and they don't like him because initially, the new boy was quite disruptive and fairly wild in class and playground, would bust up things they'd been making, etc. So DS1 feels totally torn between his new friend and his old friends. New friend 'won't let' him play with his old friends at break time, just wants to play with DS1. DS1's old friends don't like the new friend and don't really want him playing with them. He tells me all the time that his 'new friend' won't 'allow' him to play with his old friends. DS1 says 'I want to play with my old friends but that would be mean to (new friend) because he has nobody else to play with at all.' He's also feeling increasing claustrophobia because his 'new friend' just wants to be with him all the time and is very full-on - hugging, kissing sometimes, chasing DS1 if DS1 gets away from him. He's come out of school in tears about it sometimes. I've told him he's not responsible for his new friend being happy all the time, and that he is 'allowed' to play with other people, but it's not going in.
What do I do? What CAN I do? 
I'm having a word with his class teacher after half term but I'm not sure there's a lot she can do to influence playground dynamics either. If he were at a larger school with a larger pool of children, this might not be so tricky, but I'm loathe to take him out for this reason alone.