You don't mention if you too suffer from BP. All I can say is that before was dx'd with BP, I too dated someone who suffered from BP. It was intense and a real roller coaster. One never knew where one stood, and the other person's emotions would change from one day to the nex.t If your new friend has withdrawn, he is in all likelihood suffering from depression.
I would suggest you google and educate yourself as much as possible about BP and try understand what it truely is that a person experiences during BP.
Give him some room for now, and if it truely was meant to be, he'll be back once he feels better. Please don't take it personally. Suffering from BP, one often just needs to take a step back and isolate oneself from reality in order to just get through the really bad days.

Maybe sms or e-mail him, saying that you are there to support him if he needs to talk. Then you need to just be patient.
I so sorry you are going through this.