Hello, I'm happy to talk with you. I am working on your question now.
It is understandable that you would be curious about what exactly your friend's compulsion is. However, he may be very self conscious about his compulsion and may not be ready to share this yet. Keep in mind that he has already shared a very sensitive issue simply by telling you that he has OCD. This definitely suggest that he trust you enough to tell you this. If you are patient and understanding, he will most likely be able to share with you more details about his OCD in his own time. Pushing him to tell you sooner, or becoming overly vigilant to try to determine what the compulsion may be could very likely prevent him from feeling comfortable enough to share the details with you. OCD symptoms can range from mild to severe and it is difficult to tell where he may fall in this range. Either way, accepting him for who he is while encouraging him to utilize therapy for help with his disorder will go a long way to help the potential of your relationship.