What does "but it's more than one and one makes two" mean?

In the song, Wanted by Hunter Hayes, the lyrics say
“Like everything that’s green girl I need you. But it’s more than one and one makes two. But put aside the math and the logic of it. Gotta know you’re wanted too.” When he says “like everything girl I need you”, I’m assuming he’s making a reference to plants and what not because it would be impossible to survive without them. But then he says “but it’s more than one and one makes two.” That makes no sense to me whatsoever. One does not make two, it makes one. Please help me understand this.