While I cannot diagnose an individual over the Internet, I don’t believe that anything you wrote about your ex-boyfriend’s behavior indicates that he has bipolar disorder. He does seem to be moody and depressed as well as extremely jealous, paranoid, and manipulative. Jealousy, paranoia and manipulation, however, are not necessarily signs of a mental health disorder. Rather, they are generally signs of an individual who lacks self-esteem and self-confidence.
The way your ex was behaving shows that he may be currently unavailable for a relationship. By this I mean that he may have many unresolved issues that make it very difficult for him to engage in a healthy relationship. For instance, you wrote that you went to a social engagement with a male friend and he stopped talking to you completely. This is an example of an inappropriate reaction to what he perceived as improper behavior. As you said, you did not think that what you did was wrong but he did not see it that way. I do not know if attending the event with your male friend was an improper mistake on your part but his reaction was certainly inappropriate. The correct and healthy way to have approached you would have been to come to you and share his feelings about why he was upset. Instead, he decided to stop all contact with you. This behavior then prompted you to come looking for him. This is a form of manipulation.
You also said that he doesn’t like you being with other people (presumably including your friends) when he is not around. This may be related to his extremely low self-esteem but it also shows that he may be controlling. This type of behavior is indicative of an unhealthy individual.
Clearly he has problems with relationships. It took him ten years to approach you and that was after your prompting him. He may have great fear about rejection but the solution is well beyond your control. He needs in-depth counseling to help he become adept at social interaction.
If you want to help him, ask him to go back to treatment. Suggest that he get individual counseling. Counseling, if he is open to it, may help him greatly. Thanks for writing.