I have a male friend who has become pive-aggressive?

He is in his 40s and former co-worker. We were best friends (platonic) for several years, then he started becoming pive-aggressive, i.e., would give me the silent treatment. This started about six months ago but has gotten much worse lately. He will not discuss it. We used to talk a lot about anything and everything, and now this. I thought silent treatment was something kids did. I can't seem to leave from this friendship (almost like I'm a glutton for punishment). As I said before, he will not talk about why he has become this way with me. (I know for a fact that another one of his platonic female friends has made fun of me behind my back). At any rate, should I keep him on my MySpace friends list or delete him?