I'm going to just be plain with my friend and tell her that her boyfriend needs to shape up
What do you mean by shape up?
To be a little more mature
That's great you are concerned for him, but it is still none of your business what goes on between them. You might be seen as a threat if you criticize her boyfriend, like you are trying to break them up
Don't you think it's my business if he's playing her?
It's great that you're concerned for her, but I don't think it's really your business. You could try bringing it up in a casual way to see how she feels about it though.