Nintendo has no plans to include same sex relationships in the North American release of Tomodachi Life and says they're just trying to make a "playful alternate world." In a statement, they said:
Nintendo never intended to make any form of social commentary with the launch of Tomodachi Life. The relationship options in the game represent a playful alternate world rather than a real-life simulation. We hope that all of our fans will see that Tomodachi Life was intended to be a whimsical and quirky game, and that we were absolutely not trying to provide social commentary.
The internet has responded with a call for #Miiquality, asking Nintendo to include same sex relationships. If you're interested, check out Miiquality on Twitter.
Update: Nintendo has issued an apology, saying changing the game now is just not feasible, but future Tomodachi games will see more inclusivity:
We apologize for disappointing many people by failing to include same-sex relationships in Tomodachi Life. Unfortunately, it is not possible for us to change this game's design, and such a significant development change can't be accomplished with a post-ship patch. At Nintendo, dedication has always meant going beyond the games to promote a sense of community, and to share a spirit of fun and joy. We are committed to advancing our longtime company values of fun and entertainment for everyone. We pledge that if we create a next installment in the Tomodachi series, we will strive to design a game-play experience from the ground up that is more inclusive, and better represents all players.