My friend

Well. Hmm. Tell him what you think. What's going on. But be extremely respectful. Say that this is your OPINION , and that this is how it seems like. Dont try to insul thim or her, try to put it in a nice way. he's whipped and he doesnt seem to know it.

If he's a good enough friend eh should respect your opinion. chances are he wont listen to it , but it's worth a try. If he does get angry and stops talking to you, I pretty much am 95% sure that he will come into contact with you once the break up and he sees that you were right and were only trying to help him.