I cannot promise I will stay

I cannot promise I will stay
For someday I must go
I promise you I will not change
But not that I won’t grow
I promise you the here and now
And all that it contains
I promise you that brilliant sun
But only till it rains
I love you with the love I need
And that I give for free
But I can’t give you happiness
Unless you want to be
I promise I will give the truth
At least the truth I know
And I will pray that knowing this
Won’t make you want
To go