Formal:
* Mon seul et unique amour: This is the most literal translation, emphasizing the singular and unique nature of your love.
* L'amour de ma vie: This means "the love of my life" and implies a deep, lasting love.
Informal:
* Mon grand amour: This translates to "my great love" and is a more affectionate and passionate way to say it.
* Mon amour véritable: This is similar to "my true love" and emphasizes the authenticity of your feelings.
* L'âme sœur: This means "soulmate" and implies a deep, spiritual connection.
Romantic:
* Ma moitié: This translates to "my other half" and conveys a sense of completeness and unity.
* Mon cœur: This means "my heart" and is a very romantic and poetic way to say "my love."
You can also use a combination of these phrases to express your feelings more fully. For example, you could say: "Mon grand amour, l'amour de ma vie" or "Mon seul et unique amour, mon cœur."
Ultimately, the best way to say "my one true love" in French depends on the specific context and your relationship with the person you are addressing.