loving an addict is difficult and draining...........I am so very sorry you are going thru this.
your post says you dont know where to go from here..........
the fact that you and your mom drew the line with your brother was a really great start
but It may be helpful for you to read the stickys here on SR, and maybe you and your mom can find a families anon meeting or even naranon or al-anon
any family support meeting for families of addicts
Its important to know that neither you nor your mom .......can cause your brother to USE drugs nor can you make him stop using or to want help for himself........
you didnt cause it you cant control it and you cant cure it.........
stick around others will be along soon to offer more support.