If you are talking generally about your love for something or someone, rather than addressing someone directly, the correct translation is il mio amore.
If you are directly addressing a loved one, on the other hand, the correct form would be the pet name amore mio. This version is considered a term of endearment.
If you are talking about a person you love, but you aren’t addressing them directly, it is possible to use l’amore mio. However, this form is very poetic and is mostly heard in songs/poems.