"Now I`m Here" song is about his experiences during their first visit to the US (April-May 1974) when Queen were supporting Mott The Hoople. He apparently met a girl named "Peaches" at a club called Dungeon.
Touring America, [Queen] launched the album with the biggest, most exotic party they`d ever thrown - in new Orleans after their show on Halloween.
[...]
In a 1991 interview Brian said:
`I missed a lot because I was chasing someone else at the time. I was deeply in love and she wasn`t there so I went off`
Talking to Mojo in 2008 May revealed more of the road romance that haunted and partly unglued him thirty years earlier, as a young husband and new father: `I remember thinking all is not quite right. I went out looking for Peaches [as in `Now I`m Here` from Sheer Heart Attack: "Down in the dungeon just Peaches `n` me/Don`t I love her so"]. I didn`t find her, but she found me later on`. Band life and family life, he said, has benn `incredibly difficult to reconcile`.
From
"Queen. The ultimate Illustrated history of the Crown Kings of Rock" by Phil Sutcliffe.