In the lines "I used to be the kind / Who said that ev'ry girl's the same and love was just a game for having fun," the phrase "ev'ry girl" is sung to notes of all different pitches (D C Bb), giving a sense of breadth or entirety.
The same is true of the phrase "ev'ry dream" (sung to the notes E G Ab) in the line "Ev'ry dream that you have, I'll fulfill."
Each of these phrases also contains an accidental (Bb and Ab, respectively, in the song's C major), and these foreign tonalities may also contribute to this sense of breadth.
The perfect rhyme in the lines "I'll be true to you, yes, I will / Ev'ry dream that you have, I'll fulfill" provides a sense of this completeness (being "fulfill[ed]").
