In the novel, they do it (like really do it) before the brother arrives. It was hot, because the mc enjoyed it for the first time. And they skipped that part. ╥﹏╥
I READ THE RAWS AND THIS SEASON IS GOING TO END. IM NOT SATISFIED WITH THE FRICKING ENDING, WHY MAKE US SUFFER FOR 4 MONTHS, LIKE?!!! ヽ(`Д´)ノ I WANT THEM TO BE HAPPY ALREADY