There is a change--and I am poor;
 Your love hath been, nor long ago,
 A fountain at my fond heart's door,
 Whose only business was to flow;
 And flow it did; not taking heed
 Of its own bounty, or my need.

 What happy moments did I count!
 Blest was I then all bliss above!
 Now, for that consecrated fount
 Of murmuring, sparkling, living love,
 What have I? Shall I dare to tell?
 A comfortless and hidden well.

 A well of love--it may be deep--
 I trust it is,--and never dry:
 What matter? If the waters sleep
 In silence and obscurity.
 --Such change, and at the very door
 Of my fond heart, hath made me poor.

Written circa 1806-1807.

This is in the classic ababcc format.

It is quite likely that his “changed friend” was Coleridge. Wordsworth met him (after a gap of several years) in late 1806, and then for several months in the winter of 1806 when Coleridge was a guest of the Wordsworths during their stay at Colenorton, Sir George Beaumont’s house in Leicestershire.

Coleridge was back in England after a long residence abroad, mostly in Malta, trying to restore his health (which was severely affected by his being addicted to opium). Not that I’m being censorious here, he couldn’t have written Kubla Khan without that :) His health was, however, irrepairably destroyed by his drug abuse.

Dorothy Wordsworth wrote: “never never did I feel such a shock as at the first sight of him [in Oct. 1806]. We all felt exactly in the same way–as if he were different from what we had expected to see….”

His appearance and physical health were not the only things that had changed about him - his mental balance was also affected by the drugs.

Wordsworth’s grief at the state to which Coleridge was reduced shines through every line in this poem, as does his deep love for Coleridge. As he says, his grief makes him poor, robs him of his happiness.

— Suresh