I know I am but summer to your heart,
And not the full four seasons of the year;
And you must welcome from another part
Such noble moods as are not mine, my dear.
No gracious weight of golden fruits to sell
She knows she isn’t everything to her lover: just a phase in his or her life, or a certain kind of love that doesn’t exclude others . 

I know I am but summer to your heart Sonnet XXVII