Tatatonic - we all know that men are strange, complex creatures ;). I'm currently having some time deciphering the body language of a man I have not yet got close to. But sometimes it's easier to decode the intentions of others if we aren't involved with them, as in your case.
Of course, there could be a 1000 different reasons why he's ended it. The most likely is that he's gone off you (it happens) or that he simply doesn't think you two have a future together.
I know it's terribly difficult to be rational when blinded by love and desire. But I get the feeling you want someone to come up with a less-painful reason
as to why he's ended it. Perhaps he's being held prisoner somewhere? Maybe he's been brainwashed to go off you? Maybe the "friend" on the phone is his boyfriend and is blackmailing your ex to see him and dump you?
All highly unlikely. And your automatic dismissal that your ex could be gay or that he's seeing someone else. Thats more of a comfort to your ego than anything else, surely?
He could be a commitment-phobe, an emotional dud. He could have a wife and family. He could also, in the time-honoured fashion, have used you and then moved on. That's painful but it goes on all the time.
Find someone else.