Doukyuusei (NAKAMURA Asumiko)
Kusakabe thinks Sajou considers music to be beneath him--the one subject where Kusakabe excels. But one day after school, he discovers Sajou alone in their classroom practicing for an upcoming concert and offers to help. After a series of regular meet-ups, Kusakabe develops feelings for Sajou and kisses him. What follows is a story of firsts. This is a sweet love story, a bit sad at points, but ultimately happy. Doukyuusei was made into an anime, which is absolutely lovely and follows the manga to a T. The voice actors did a fantastic job. It also has two sequels and a side story, which I tagged "Doukyuusei" so you can find them.
Sotsugyousei
The sequel to Doukyuusei, in which Sajou and Kusakabe have to face their upcoming graduation.
Samishigariya no Love Letter
One afternoon, a boy finds a chocolate tin in his bag and begins to correspond through it with a boy he's never met. Childhood friends finally start dating. (The one where the older one is oblivious and thinks they're "practicing" and the love of his life is tall and blond with piercings, and everyone is scared of him. This is the story with the end comic where their parents have been in support of their relationship since they were small and had already looked into moving the families together and planning a wedding.) Ten years after his five-year-old friend proposes, a man has to decide if he wants to honor the promise that they'd one day marry. I skip this one on reread.
07 Ghost
Teito Klein is sixteen, orphaned, and cannot remember much of his past. Until recently, he'd been a battle sklave used by the Barsburg Empire, but for the last year he has been enrolled in a premiere military academy. There, he meets his one and only friend, Mikage Celestine, and dazzles his professors (and makes some enemies) with his command of zaiphon, a powerful energy force. Teito and Mikage are two of only a handful who pass exams and their future looks bright - until Teito accidentally overhears his name in a conversation about the Eye of Mikhael - a powerful weapon - and the death of the King of Raggs, the kingdom that fell during the war ten years earlier. Believing the king may have been his father and newly afraid for his life, Teito flees the academy with Mikage's help and is forced to leave him behind. Some time later, an exhausted Teito falls unconscious on his hawkzile, a small flying craft, plummeting to his would-be death. He is saved at the last moment by Frau, one of three bishops from the nearby District 7 church, who give him sanctuary. Teito is overjoyed when Mikage finds him in District 7, but his happiness is short-lived when it’s revealed Mikage is under the control of the empire in an effort to recapture Teito. Devastated by the death of his only friend and grasping at information revealed to him by fragments of memory, Teito trains to become a bishop and is apprenticed to Frau, a seemingly young and perverted man who is actually one of Seven Ghosts sent by God to search for and destroy the evil death god Verloren. With Frau at his side, Teito leaves District 7 on a pilgrimage to Seele - a place he’d travelled to as a child with Father Kreuz, the bishop who had raised him. He believes Seele holds the answers he is looking for about the death of his father and the destruction of a kingdom. 07-Ghost is a story of loss, of perseverance, of grief, of hope, and above all, love. The love between Teito and Mikage is fraternal, but that love is a driving force behind this story, and Teito’s love for the other people in his life carries him. In my opinion, the closest to romantic love we see is between Teito and Frau during their journey to Seele. The 100th chapter is not included in the US translation released by Viz. The story ends after Frau’s final line about a picnic.
Hidamari ga Kikoeru
Kohei is hearing impaired and isolated as a result. People mistake his silence as elitism, so he's left out of activities and feels like he's bothering people if he asks them to repeat what they've said. But one day, a loud, carefree boy named Taiichi falls onto the roof where he's eating his lunch and befriends him. This is a really gentle and lovely story about first love, but it's more about friendship and trying to understand and bridge differences between us. ETA: All volumes of this manga are licensed in English
Hima na no de Hajimete Mimasu.
Rin and Maki are inseparable childhood friends whose relationship evolves from close to intimate when they start living together. Maki is completely devoted to him, but Rin - who initiated things - is worried what other people will think. This is the one with the sweet boyfriend with long hair who is so terribly, terribly in love. They slap each other a lot. Some readers took issue with it; I agree it's not something you should do in your own relationship, but it didn't ruin the story for me.
Junjou
A man is reunited with the guy he'd been in love with in high school, and they fall into a physical relationship that grows serious, but they have to navigate jealousy and family issues. There's a movie version that I don't care for, but I really enjoyed this manga. I've read it three times - and the third time was probably my favorite. Kurata is a jackass when we first meet him. He's never understood the feelings he has for Keisuke, going back to high school, and sleeps with him to confirm that Keisuke had once liked him. He continues to use him for sex - often forcing it - but eventually falls in love and experiences a pretty significant personality change. He's sweet by the end, and Keisuke calls him out on his terrible behavior and breaks up with him for a while - I liked that. Includes lots of cute oneshots about their life after moving in together.
Dear Green: Hitomi No Ounowa
This is long, so it's good for a cold day or spaced across a week. Childhood friends grow into something more over a period of years. Great female best friend character as well.
Sono Te No Netsu Wo Kasanete
The one with the ceramic artist and the restaurant owner!
Hana no Mizo Shiru