What is the main conflict in Bright Star! Would I Were as Steadfast as Thou Art by John Keats?

The problem facing the speaker in this poem is that he would like to stop all change, to freeze things at one particularly wonderful moment, but he realizes that doing so would be the opposite of living life, that life is change, even when that change is something as small as the motion of his lover's breathing. Keats, aware of his impending death from tuberculosis, would naturally have a reason to fear change, and he would have wished to stop the clock before his life ran out of minutes, but, as he admits here, doing so would mean missing out on life's pleasures.