Haru Natsu Aki Fuyu

Haru Natsu Aki Fuyu is a Girls Love manga written by Eiki Eiki and illustrated Zaou Taishi, a duo best known for their (many, many) Boys Love mangas. The story is set in St. Teresa's school for girls and consists of five individual stories focusing mostly on the growing romance between two pairs of schoolgirls, although one story focuses on the adults and another, on two unrelated girls.

There's some focus on lesbianism.

The stories, in order, are:

Expressions of Love: New student Akiho has to deal with some mixed feelings for her best friend Haruka, a popular girl with a tendancy towards Skinship Grope.
She-Wolf: Shrinking Violet Fuyuka transfers into St. Teresa's, looking forward to life in an all-girl environment. Unfortunately, she becomes the latest target of the local Memetic Molester, Natsuki "the She-Wolf".
First Kiss: Focuses on Reiko and Ayano, the school counselor and teacher respectively, as Reiko reflects on their own days as students together, and how their relationship has changed.
Little Red Riding Hood Strikes Back: A followup on "Expressions" and "She-Wolf", Akiho helps Fuyuka try to clarify the nature of her relationship with Natsuki.
Spring/Summer/Winter/Fall: The conclusion for the two student couples, featuring a Beach Episode.
Her: A side-story; Two girls, Inoue Chiharu & Aida Miho, have feelings for each other, each convinced they're weird for it but planning to seduce each other at the exact same time.

There is also a borderline-Hentai "doujin" by the original authors titled simply HaruNatsuAkiFuyu, exploring the two main couples' intimate moments.

Tropes used in Haru Natsu Aki Fuyu include:

A-Cup Angst: Haruka has a baaaad case of this. She later decides she doesn't care, as long as she has 'Akiho's breasts.'
Bait and Switch Lesbians: Arguably deconstructed in "First Kiss", given that Reiko and Ayano dismiss their romance as a simple Romantic Two-Girl Friendship, realizing years later they've been in denial about it the entire time, and were both unable to make a move because they thought the other had been sincere in moving on.
Beach Episode: "Spring, Summer, Winter, Fall" involves a beach vacation.
Beta Couple: Akiho/Haruka to Fuyuka/Natsuki. Ayano/Reiko to all four of them.
Beware the Quiet Ones: In bed, Fuyuka is waaay more aggressive than you'd think from her shy everyday behavior, as Natsuki has to discover the hard way. They later decide to determine who takes the lead with Rock-Paper-Scissors.
Can't Act Perverted Toward a Love Interest: Natsuki falls into this in "Little Red Riding Hood Strikes Back", confusing and dismaying Fuyuka, who finally wants Natsuki to act perverted towards her.
Cast Full of Gay: Well, all the girls, anyway.
Deadpan Snarker: Akiho.
Does Not Like Men: Fuyuka intentionally switched to an all-girl's school to get away from men; we find out the reason for this later.
Finger-Suck Healing: In "First Kiss".
Gayngst: Generally averted, although some of the girls do have anxiety their feelings might not be real or reciprocated.
Handsome Lech: Haruka and Natsuki are both extremely pervy, but also well-liked due to being hot and athletic.
Meaningful Names: Haruka, Natsuki, Akiho, and Fuyuka.
No Periods, Period: Averted in "Spring, Summer, Winter, Fall".
One-Gender School: St. Teresa's.
Rape and Switch: Both Natsuki and Fuyuka have an aversion to men due to traumatic past experiences, although it's never claimed that this is the cause of their lesbianism.
Double Standard Rape (Female on Female): Natsuki seems to believe in it, at least, in the part that women cannot hurt other women.
Romantic Two-Girl Friendship: Fuyuka worries her relationship with Natsuki is this despite being sexually attracted to her, while Reiko and Ayano believe their past relationship was this. Averted in both cases.
Schoolgirl Lesbians: And how.
Situational Sexuality: Discussed in "First Kiss".
Skinship Grope: Haruka's M.O.
Shrinking Violet: Fuyuka, although she shows shades of Covert Pervert after opening up to Natsuki.
Sugar and Ice Personality: Akiho is cool as a cucumber most of the time, but she can get more emotional around Haruka, particularly when she finally expresses that she doesn't like it when Haruka gropes other girls.
Zettai Ryouiki: Haruka is grade B to A.