Well, I'm probably going to regret posting this. This interpretation is exclusively based on my associations and nothing else, but I can't read it in any other way.
To me the lyrics are basically him speaking either to himself or a man close to him, or both, it doesn't matter who exactly the addressee is.
The childhood imagery evokes memories of a happier, simpler time but what really stuck out to me is the "a sick boy must be treated" line. Boyhood for him was also a time when homosexuality was still often seen as a sickness. Could also refer to something else, he certainly felt "sick" for just being "different" in general, but since homosexuality is often an underlying theme in his work, it was the first thing that came to my mind regarding that line.
So his pals abandon him eventually because of that "sickness"/being different and the only safe harbour is at home with Ma, which leads to a life of isolation.
I think the girl of his dreams is more a figure of speech. A metaphor for an ideal that every man is supposed to strive for but that girl could be anything or anyone. He just has to realise that. "There is something that you should know"... that "thing" you've been looking for is here right before you but you can't see it.
I think considering the timeframe and the context of other songs on Southpaw Grammar and, of course the title, it also works as a kind of pre-/mid-break up song. Very fitting that he described it as a song
that belonged "only to that moment in 1995, and none other".
It's one of my favourite songs (of Morrissey or any other band or artist). It just contains so much weight and emotion and the lyrics manage to convey this with very little effort. The picture it paints in my head is so vivid and clear, but it's sort of hard to describe.
That's one of Morrissey's biggest strengths in my opinion - to tell a whole life with just a bare minimum of words.
What really kills it for me is the "Help me" towards the end.