Koiiro Devil

From Girls' Generation Scanlations:

He's perverted, malicious, a devil that calls himself 'Ore-sama'.
His true character is -? The Demon King, Char, from a parallel world called Avalon, fell in love with the daughter of a shrine, Hashiba Rin. Both their hearts and bodies have been entrusted to each other, but a first love, Shou-chan, confesses to Rin-?

From Starry Heaven:

Hashiba Rin, the daughter of a Shinto shrine, fell in love with the demon king, Char, who came from a different world called Avalon. They shared their love with their body and mind, but Rin's first love, Shou-chan, confessed to her and---?
Following Char and Rin's meeting, "Honey Colored Devil," the popular serialized in heaven love magazine appears with an extra chapter<3

from Renta!