Formal/Romantic:
* E ke aloha o koʻu puʻuwai (literally: "the love of my heart") - This is a very poetic and romantic way to say "my sweetheart."
* Koʻu aloha (literally: "my love") - This is a more general term for "my sweetheart."
* E ke aloha nui (literally: "my great love") - This is a more passionate way to say "my sweetheart."
Informal/Affectionate:
* Koʻu pōkiʻi (literally: "my little one") - This is a term of endearment often used for a loved one.
* Koʻu puʻuwai (literally: "my heart") - This is a more informal and intimate way to say "my sweetheart."
Other options:
* Koʻu ipo (literally: "my lover") - This is a term that implies a romantic relationship.
* Koʻu hoa aloha (literally: "my love partner") - This is a more modern term that is gender-neutral.
The best way to choose the right phrase is to consider the context and your relationship with the person you are addressing.