I LOVE Kodama Naoko's work and this is NOT NTR. Akane was frustrated by the fact that the girl she liked got a boyfriend, whom she knows is not right for her, and with the help of good ol' alcohol went for Kotori and Kotori reciprocated and now they're together. All that's left is the clean break-up. AkaneXKotori, we all know that Mr. Boyfriend is a throw away character/plot device used to further their actual yuri relationship.