My Tsundere Childhood Friend... I Got A Girlfriend, And She Says She's Training Me To Improve My Premature Ejaculation And Has Jealous Self-promotional Sex With Me... Airi Nagisa

Childhood friends Nagisa and Higashi have always been a bickering pair since they were kids. Now a high school student, Higashi starts dating a female classmate for the first time and is on cloud nine. Behind the scenes, Nagisa secretly receives a consultation from the girlfriend, who says, 'Higashi is struggling with premature ejaculation.' Despite her complicated feelings, Nagisa offers to be Higashi's practice partner for blowjobs under the guise of 'training'... Is it an extension of teasing, jealousy, or something else?