Low self esteem

Hi, 

My son (8) was diagnosed in Jan but these issues have been happening for about 6 months now and are occuring more often. 

Sometimes when he's told off or his brother shouts at him, he cries, shouts and then it goes worse. He says things - nobody loves me, everyone hates me, I'm dumb, I'm stupid, I wish I was dead, I want to be dead, I have no-one. 

This situation can take up to 45 mins for to for him to calm down and he will go back into this state if I try to talk to him about it once he's calm.

I've put in a referral for mindmate, which will take ages. 

Where do I go from here? It's heart breaking.

Thanks.