Hi Pelin, you would say, "my love for it grows every year." In this case, the preposition for is appropriate because you are indicating the motive or reason , that is, the "it" that your love grows for or benefits from every year. You did not share what this "it" is. However, if you said this sentence to me, I would either already know what you're referring to or I would ask you to tell me what "it" is and explain the reason why your love for it grows every year. Hope this helps!

My love FOR it