My bro got the covid vaccine and feels so terrible he doesn't want the 2nd shot, but I read serious problems may occur without 2nd shot, T/F?

it means the vaccine is doing its job well. He needs to get that second dose. The symptoms hes feeling rn will go away. 

i got both shots and now i wont get the damn virus

No.  It just means that if the vaccine provided him protection, it will provide him less protection than if he got both.

i think he should ask his doctor about it

Talk to your doctor about that one.   I've never heard anything about that.   People with chronic severe allergies are sometimes known to have adverse reactions. 

Nada mas.

false................................

Without the second shot, the first one just becomes ineffective.