The very first sentence also introduces the theme of loneliness: 'I wandered lonely as a cloud.' Here this simile reminds us of how empty a sky is, and therefore how empty the person is. There is a part of them that is not fulfilled- this is having a companion. The fact that it is an obscure simile; a person is compared to a cloud; draws attention tho the sentence and emphasises the theme of loneliness.
The sentence 'For oft when on my couch I lie' also suggests lonleiness. It shows that the poet is regularly lying on their couch. This perhaps suggests that, often, they have got nothing better to do- nowhere to go, no-one to go out and see, and that they are usually just alone on their couch.
The poem altogether and what it is about suggests loneliness. The poet spends most of their time just with the daffodils- it is like the daffodils are the poet's only true friends, and that most of the poet's time is spent in the 'jocund company' of the daffodils. He is lonely and so seeks company in flowers and plants as he perhaps does not have many friends of his own.
The poet does not seem to gain much pleasure from his normal daily activities- seeing the daffodils dance seems like the highlight of his day:
'And then my heart with pleasure fills
And dances with the daffodils.'
He perhaps finds joy in the simplest of things such as flowers as he cannot find hapiness in his day-to-day life. This suggests he does not have many friends, as friends would make him very happy, and then the daffodils would be an insignificant pleasure compared to the company of friends. The poet tries to find joy out of nature as he cannot seem to find it elsewhere- he is