Janie's first husband is chosen for her. She has little say in the matter of this marriage, and complies with her grandmother out of respect. As she matures, her self-awareness increases, and she finds in Jody-therealization that there is more to life than her own backyard.
While her marriage to Jody turns into an empty shell, she gains a backbone, and continues to develop her sense of self
Janie and Tea Cake have the closest example of a true partnership. Janie has finally been able to define what a fulfilling relationship should be, and follows her heart-and does not care about the public's perceptions. This is different than her other two marriages.
The final sentences are her realization of the journey she has taken, that although Tea Cake died, she achieved her goal of a satisfying relationship-and that he will still be a part of her in spirit.
To simplify the above, only Tea Cake allowed Janie to truly express herself freely.