SUMMARY (SPOILERS AHEAD): Continuing right after the previous part, when Eri brings up the topic of what happened last night Yuuji affirms that due to the alcohol he doesn't remember anything. She then tries to call her mother for advice, and gets the usual "marriage is complicated" and try to use those difficulties to further know each other.
Again the molesting repeat that night, and finally Eri musters up the courage to confess to her husband what happened. Making a show out of it, he brings Satoru and makes him apologize even considering going to the police. Eri argues against that, accepts Satoru's apologies...and up we go again with the post-dinner activities.
Second half jumps back in time and confirm the hints from the first doujin: everything was a setup by Yuuji himself. The day after the first incident he confessed to Satoru his feelings of inadequacy when it comes to pleasuring her wife, the way it was affecting their relationship and how seeing her expression of pleasure last night make him realize all that.
So he gives Satoru the permission to go ahead and set up everything we've seen so far. Netorase ensues, and seeing her husband condition Eri accepts Satoru completely to the point of ending up going without a condom (even though that wasn't in the initial agreement between the two colleagues). Finally, as indicated with those last wordless pages, we reach a happy ending for the three of them and their newly discovered hobby.