Okay, if you wanted to know, i have three favorite anime couples, and they're all tied in first place... so here they are

Fakir+Tutu/Duck

Kamina+Yoko (3rd saddest)

Simon + Nia (Saddest)

In each show though, None of them can actually bet together forever, either one dies ( Nia and Kamina) Or one turns into a duck for the rest of her life.. (Tutu/Duck)