I'm going to stop taking care of my brothers dog
Is there a specific reason for doing so?
Yea, I can not take care of the dog and myself.
Making time to prioritize yourself can be difficult, but very important. Talk to your brother and explain that you can't make the time to take care of his dog anymore and you have to worry about your life.
Whatever, I'm going to give him back his dog.
It is a mature decision to decide to not adopt the dog if you need to focus on taking care of yourself. It is much better to be honest about this fact than to take on more than you can chew. Having a pet can be a lot of work.