Love's Fitfulness

You say that I am fitful. Sweet, 'tis true; 
But 'tis that I your fitfulness obey. 
If you are April, how can I be May, 
Or flaunt bright roses when you wear sad rue? 
Shine like the sun, and my sky will be blue; 
Sing, and the lark shall envy me my lay: 
I do but follow where you point the way, 
And what I feel you doing, straight must do. 
The wind might just as well reproach the vane, 
As you upbraid me for my shiftings, dear: 
Blow from the south, and south I shall remain; 
If you keep fixed, be sure I shall not veer. 
Nay, on your change my changes so depend, 
If ends your love, why then my love must end.