Hello, Green Days

The first time his feelings are returned, the first time having a boyfriend and the first time truly being in love... Tomo is a shy botany graduate student who is scared of love. When he sees Yoji, a rather intimidating new lab member, barely making ends meet, Tomo suggests Yoji move in with him. Despite appearances, Yoji is very kind, and Tomo begins to value their time together. Just then, Yoji suddenly confesses to Tomo, and he accepts. Yoji treats him with lots of love and kindness, but this being the first time dating someone, Tomo struggles, not knowing how a boyfriend should act...

(Source: MangaPlaza)

Note: Includes one extra chapter.