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

My childhood friend Nagisa and I, Azuma, have had a relationship since forever where we can't open our mouths without fighting. As a high school student, Azuma starts his first-ever girlfriend relationship with a female classmate and is on cloud nine. Behind the scenes, Nagisa secretly receives a consultation from the girlfriend saying, 'Azuma is struggling with premature ejaculation.' Despite harboring complex feelings, Nagisa offers to be Azuma's practice partner for blowjobs under the guise of 'training'... Is it an extension of teasing, jealousy, or something else...?