Welcome to the Wefugees Community and thank you for your question.
I don't see any reason why your brother's decision to voluntarily leave Germany should have any effect on your (residence) situation in Germany. Your asylum cases have been assessed individually and since you are even both (I assume) older than 18 and not dependent on eachother, there is no direct connection between you in legal meanings.
Do you agree dear @mbe-on_Zsigó?
In any case, please don't hesitate to get back to us with any further questions.
All the best,