Dekiai Kareshi wa Bucchouzura shite Yattekuru

Office worker Yura has been living with his super cold and unfriendly daycare teacher boyfriend, Kaji, for six months. Every time Kaji unexpectedly smiles, Yura can’t help but feel happy.
However, there’s one unexpected problem—Kaji is a total stamina monster, and Yura just can’t keep up in bed! Determined to satisfy his boyfriend, he pushes himself to improve… only to be suddenly rejected.
Has Kaji already grown tired of him…!?

(Source: Houbunsha, translated)

Note: Includes an extra.