Not clear on the question, but….
If you're asking how to say this phrase and not specify the gender of the person you love, the most direct formulation can't really do that. It's either "a" or "o." Presumably even word "agender" in portuguese also takes an "a" or "o" [Note: glad to be instructed otherwise if that's not so.]
Remember, however, that if you set up the phrase to refer to something other than a person, then the "a" or "o" could refer to something other than the physical gender of the person involved.
So for someone of no specified gender, you could somehow construct it to refer to "the person I love" and as "the person" is "a pessoa," the referent would be "a"--not because the person is necessarily female, but because the WORD "person" has grammatical female gender.