The phrase "what I feel for you" suggests that the speaker experiences a deep and special connection with this particular person. It signifies a profound emotional bond and affection.
The contrast provided by "what I do not feel for anyone but you" emphasizes that the emotions the speaker experiences for this person are unparalleled. It implies that their love and attachment are so singular that they don't experience the same depth of feeling for anyone else.
In essence, this statement beautifully conveys the idea of a love that is exceptional and incomparable. It highlights the exclusivity of the emotional connection, emphasizing that the person holds a unique and irreplaceable place in the speaker's heart and life.