You can be supportive of a loved one with bipolar disorder without supporting his addiction.  Unacceptable behavior is unacceptable no matter whether it is bipolar or addiction.  Perhaps learning the difference between empathy and sympathy first can help.


Being sympathetic would pull you too far into the addiction and your loved one's unacceptable bipolar behavior.  On the other hand, being empathetic would mean showing your understanding, unconditional love, and support in his struggle toward recovery (as long as you don't let it become codependency and thus pull you into the addictive process).


Remember that addicts (as well as people with bipolar disorder) can be very manipulative, and when they are in active addiction and/or in a bipolar episode, they will do anything to get their drugs. Don’t allow yourself to be pulled into this. You can be empathetic (understanding, supportive) without allowing yourself to be used.


You also don't want to be an enabler – one who keeps helping pay the car payments and rent, thus assisting your loved one to stay on their path of addiction and dependence on you.  Enabling at its worse would be doing things for your loved one that they can do for themselves.  If you continue to do this, it can lead to codependence, and you don't want that.


Because your loved one has bipolar disorder and is an addict, he is trying to run away from reality. He does not want to face up to things as they really are. And one of your biggest challenges will be to help him face reality as it is. Alcoholics Anonymous calls this “facing life on life’s terms,” and it works just as well for bipolar disorder as for alcoholism and drug addiction.


Your loved one may want your help, but at the same time, he may seem to push you away. This is normal behavior for an addict and someone with bipolar disorder (especially during an episode). Remember, he is going through an internal struggle because of his addiction and bipolar disorder. The addiction itself has a very strong physical hold on his brain, and he feels that he needs that “fix” to keep himself going, and the bipolar disorder has a very strong emotional hold on him as well. 


Remember that he can reject your help without rejecting you. He still needs your love and support, even as he rejects your attempts at intervention.


On the same token, remember that you can unconditionally love him and give him your support, even as you reject his addiction and unacceptable bipolar behavior.  You can reject his addiction without rejecting him.  You can also reject his unacceptable bipolar behavior without rejecting him.