I'm going to tell my friend all of my concerns about their relationship.
Why would you tell them your concerns about his own relationship?
Because we fit each other's needs and we generally enjoy each other.
Just because you feel close with your friend doesn't mean that you get to dictate his relationships and who he spends his time with. You need to leave him alone and allow him to enjoy his time with his significant other.
It's all good, I want people to do the same for me in relationships. And not dictate, advice. Just tell the truth and be honest.
Fair enough. I don't see a problem with that. Careful though, your friend might not agree with you or me.