I just think the end was funny. Even though I love threesome stories, this ending made me angry. I laughed so hard when sensei said "I love both of you". I think the ending was not satisfying. The teacher must have never said that, he must have cursed them and break their hearts. I wanted a bad ending (bad for Ookouchi and Shouta), even though I think this ending is still a bad ending (for the teacher).
Now we will see how Shin is angry. Attitudinize time.