 If you liked
Itoshi no Goshujinsama
|
 ...then you might like
Ookami Shoujo to Kuro Ouji
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In both mangas, there is a couple with a master-dog relationship. Both of the heroines are usually ignored by their boyfriends, much to the heroine's chagrin. Also, with the entrance of another guy, things start to crumble between their relationship, but things end up normal in the end. The love interest is also somewhat of a sadist, and teases their girlfriend too much.