I don't believe "I Won't Share You" is about Marr. I read nothing in the lyrics that indicate that at all. That story just seems to have come out of people just looking at the title and wanting to paint Morrissey as some kind of obsessive monster when it comes to Marr.
I agree. It happens to be the last song on the last Smiths album so it seems to be brimming with subtext. It's not. Because "Strangeways" was the last album several songs were interpreted rather strangely, like the line "It's crap, I know" on "Death At One's Elbow", which was interpreted by a critic whose name escapes me as Morrissey's candid admission that his lyrics weren't up to snuff and hence The Smiths had run their course.
However, a "final message" case could be made for "I Keep Mine Hidden", which was the last Smiths song. I think Morrissey was probably directing those lyrics at Johnny.
I agree with both of you about "I Won't Share You". I also find it amusing that one of the songs where Morrissey most directly specified gender ('she') is the one people insist on being about Marr. You don't hear people insisting that "He Knows I'd Love To See Him" is about Linder, do you?
You are probably right about "I Keep Mine Hidden", but Morrissey probably didn't intend it as a last message. Right until the end, he didn't seem to think The Smiths were breaking up.
I would add "Hand In Glove". I usually think "Break Up The Family", too, but sometimes I'm not so sure about that one-- maybe it's directed at several people in his past.
Morrissey said it was about the group of friends he had in his early teens.
"The song 'Break Up The Family' is strongly linked with 'Suedehead' and 'Maudlin Street', that whole period in 1972, when I was 12, 13. 'Break Up' is about a string of friends I had who were very intense people and at that age, when your friends talk about the slim separation between life and death - and you set that against the fact that this period of your youth is supposed to be the most playful and reckless - well, if you utilised that period in a very intense way, well, that feeling never really leaves you."
Did you all consider the family a bad idea?
"No, we didn't feel that at all. The family in the song is the circle of friends, where it almost seemed, because we were so identical, that for anybody to make any progress in life, we'd have to split up. Because there was no strength in our unity. And that's what happened, we did all go our separate ways, and quite naturally came to no good. I saw one of them quite recently, and it was a very headscratching experience."
Because he'd turned into the complete opposite of what you all had been?
"No, not at all. Which is the confusion."
And your gang, were you outcasts, victimised by "The Ordinary Boys"?
"Yes, but half of it, I have to confess, was the effect of deliberate choosing. We chose to reject the normality of life, and be intense and individual."
http://motorcycleaupairboy.com/interviews/1988/songs.htm
I think it was "Angel, Angel" although I'm not sure-- and anyway I think someone said "Is this about Johnny?" and he didn't deny it, or gave a vague yes or something. As you said he's not that forthcoming.
Actually, he outright said it was about Marr. I'm not sure which interview this quote was originally taken from, it appears in a Mojo article:
Morrissey: Angel, Angel, Down We Go Together was written with Johnny Marr in mind and it is the only song that I have written with him in mind, post Smiths. I saw him in the music industry being used and being manipulated and I felt I was in a similar situation.