How do I get past this feeling of extreme dread and helplessness because the reality that there is very little I can do... And I kind of know I should not be so triggered by it. but I cant fight it
Have you thought about CBT? There are really useful exercises you can do that help you to focus away from anxiety and difficulties and get on with the job.
Because at the end of the day, your job is to help your ds to get over disappointments as painlessly as possible, to develop an attitude that he can cope and that feeling a little bit upset doesn't mean something terrible has happened.
The strengths you help him to develop now will help him get over far greater disappointments later on. Sooner or later, some girl (or boy) will ditch him, he will miss out on an opportunity he wanted and felt he deserved, he will be lonely- as we all are from time to time. But if he has that inner confidence he will get over it.
It doesn't have to be massive things: littledoll's response is perfect:
"you would be much better just saying 'sometimes you get invited, sometimes you don't. Let's go to the park instead and play on the swings and slides!'"
If he trusts you to stay strong and cheerful, he will feel able to tell you of his disappointments. If he grows up thinking you will get terribly upset, he will soon start trying to protect you. And that means he will lose the support he needs.
I am currently waiting for a telephone call from my (disabled and mentally ill) dd who has been for an interview regarding something very important and intensely competitive. I am not expecting her to have succeeded and she probably doesn't either. But she knows she can ring me, because she knows I don't need protecting and I will make her feel better about it, whatever the outcome. And yes, I use CBT.