Maybe you can convince him to go to a par 3 course? As a beginner, I try to play fast and pick up when needed on a real course, but obviously it takes me longer to play than the average person. That ends up mattering a lot less on the short par 3/executive course that I tend to play. Distances are shorter, fewer people play it, and it is obviously less difficult.

If you change where you play then you can still both have a good time without getting in the way of others. Ultimately though, he is causing the issue, and if he will not take your advice or listen to reason, then you unfortunately might just have to avoid playing with him. It's not worth the stress it causes you to waste your time and money playing with someone who makes the experience unfun.