There is a dialogue log button on the bottom left of the screen when you are in a conversation, you can use it to see which options he picks or if he skips some lines, although I think it automatically closes if the conversation ends. I like the idea you suggest and using the dialogue log can harm the pace and ruin the immersion for you, but unless they change how multiplayer conversations work, it is better than missing parts of the conversation or asking your friend all the time.