We've had this with ds2, and I so feel for you. If it is any consolation, it flares up (ds's perception of being left out) and then dies down, because he has a lovely quality of being interested in things, and focusing entirely on things that do interest him and people who DO care for him, and forgetting his other troubles (other people and how they react to him)
I think because we are older and wiser we take on responsibility for all their sorrows and forget that sometimes they just discharge their emotions and feel much better for it, until the next time 

I think you should ask the school to log any incidents of him having difficulties in the playground as matter of urgency, because sometimes that can speed up a CAMHs referral. We certainly found that the school had to give an extremely negative version of ds's behaviour in school in order for him to be seen. They warned us that they needed to show his behaviour on the worst day not the best. And you need to do the same.
Also in the meantime school should be taking some responsibility for his social communication difficulties. My son's primary arranged a buddy for lunchtimes when he was being teased. They had a friendship bench in the playground. They had a small club where they did Lego, and he was able to interact without the same pressures of a large playground. There was also a Nurture group, where he went and was part of smaller group.
I used to say that my child was so upset he wasn't coming in unless something was done to support him, and fear of dipping attendance figures made them act very promptly to provide this support. I rang up the SENCO and spoke to her directly on these occasions, where I felt he was so upset about the playground situation.
You may feel that holding him close is of little help, but it is such a powerful way of reminding your child you are on his side, and that he can rely on you through thick and thin and that honestly is worth an awful lot.