That is quite a dilemma. But, I think your priority, given the situation, is to protect yourself first. If your brother is getting you back into drugs, I think you need to stay away from him.

I know you feel it's your duty to support him, but not at the expense of your own health and well being. He is an adult, and needs to take responsibility for himself.

Maybe you could help him make arrangements to stay elsewhere ? Friends, family, etc ? Not with you if he's going to tempt you with drugs.