Annoying clingy cat?!?!? need help he is driving me crazy!!!!?

It will be because his brother is gone. As someone else said he may not realise he has died and may be trying to find him. If he knows it may be a product of anxiety. Mother cats that have their kittens taken will also do this. It will usually sound a little different than their normal meow and it is anxiety related. I have seen this first hand with my own cats. Just give him plenty of love he will stop soon.