Things like this does happen when you mix friendship with a profession no matter what the profession is.(which is why there is an ethics law with most professions ie therapy, doctors and so on where it is a rule not to mix friendship with the profession so that the work side does not interfere with the professional side of things.

Talk with your friend and explain your feelings so that the situation doesn't escalate causing the two of you not only your professional relationship but also the friendship relationship.

Its kind of like my having a friendship with my ex therapist SKR. During therapy time we had to make sure our friendship did not interfere with therapy time and now that she is no longer my therapist we have to make sure our time together is friendship not therapy. If the two collide it could make for a disaster. At one point when one friend - SKR - saw the two starting to collide she had to point it out to me right then and there. That way the situation wouldnt effect our friendship and wouldnt effect my therapy time with my present therapist LL.

If you and your friend can't keep friendship and business separate you may end up having to go through a different realator in the end but the situation needs to be dealt with so that it deos not effect the friendship..