When you need to have a difficult conversation, one of the keys is to de-personalise it. You want to avoid them feeling attacked by you. You want to avoid it turning into a “relational issue” (simply because this is an easy way to get you off their back).
So grab a pen and paper, or a white board and a marker and write down the thing you want to talk about. This will take some planning on your behalf. For example it might be, “I want to have a discussion with you about how you can love your wife better.” Or, “I really want to talk to you about how you’re going to put your porn addiction behind you.” Or, “Lets talk about how you responded to Bob last week.”
And you write down “How can Tom love Tara better?”, “How can Tom put porn behind him?”, “How you responded to Bob last week.”
I know it seems a bit odd, but now it’s not YOU asking them this question, its the paper. The piece of paper becomes the “antagonist” and you and the person can work together to answer the antagonist piece of paper. It’s the 3rd party in your conversation.
And so when they go off on tangents or try to change the topic, you can redirect them back to the paper, “Tom, we still have this question in front of us… I’m on your team… What are we going to do?”