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
Have I, nor any wise and wintry thing;
And I have loved you all too long and well
To carry still the high sweet breast of Spring.
Wherefore I say: O love, as summer goes,
I must be gone, steal forth with silent drums,
That you may hail anew the bird and rose
When I come back to you, as summer comes.
Else will you seek, at some not distant time,
Even your summer in another clime.
Clime = climate/region.  The speaker is essentially saying that her “summer” lover will move on soon. 

I know I am but summer to your heart Sonnet XXVII