What can I do if I am charged with aiding and abetting?

Here is my scenario. A friend of mine whom I have known for many years called me one day. He told me some people owed him some money and he was to meet with them so they could pay him. He told me he was afraid to go alone and had a "bad feeling" about these guys. He told me he was afraid they might rob him. He asked me to accompany him just to make sure nothing went wrong because he was scared. I once considered this guy to be like a brother to me and therefore felt sympathy for him because I care for him. He made me believe he was in danger. I agreed to go with him but in my own car. I remained about 500 feet away from him and was unable to see what he did when he met these guys. It turns out when it was all set and done he told me "MAN THEY DIDN'T HAVE MY MONEY, BUT THEY PAID ME WITH SOME XTC PILLS. I did not see the transaction nor did I ever see these so called "pills". I followed him out in my car because he appeared to still be afraid. One month later I'm called in by police for an interview and they tell me they are going to charge me for aiding and abetting PCS. My so-called "friend" was actually an informant who was in trouble with the law and threw me into his mess for a sentence reduction by telling them I was his partner in crime. I have never been in trouble with the law. I might be guilty of bad judgment, but a criminal I am not. He used me and they lied to me to get me in that situation. They took my weakness for granted because they knew I really cared for him like a brother. Two weeks later after the interview I am still here living in turmoil. What can I do? Make note I never knew he was there for a drug transaction nor did I see the drugs.