The correct answer was Michael/Ginny.
Without a word this damsel ran
redwood7: We never heard about it until Hermione told us...
me: And Ginny is, of course, the damsel of CoS.
Into the arms of her “Handyman.”
me: OK, I admit this was a bit obscure. This is an allusion to an old song called “Handyman” that was recently covered by James Taylor. Does anyone else think it describes Micheal Corner well? I mean, he’s picked up the pieces of hearts Harry has broken twice now.
Like Orion he was treated.
redwood7: Michael (as we see above) drew the ire of Ginny's brother Ron. Bluemeanies explained this well already.
bluemeanies [comments in brackets mine]: The hint of Artemis and Apollo gave me a new idea. The guy [Orion=Michael] used to date a certain sister [Artemis=Ginny] and her brother [Apollo=Ron] was none to pleased.
In the end, he was defeated.
redwood7: I took this as Michael was defeated when Gryffindor (and Ginny) beat Ravenclaw in the final match.
About this ship there’s no debate;
redwood7: Because dear St. Hermione informed us it was true...
me: You know, since writing this riddle, I have learned that there actually is some debate about it. In fact, I seem to recall a nasty little argument breaking out on the Orange Crush thread, because some folks were trying to say it was less serious of a hook-up than it was made out to be. *shrugs*
It may be canon, but it isn’t fate.
redwood7: It isn't fate because Ginny's fate lies elsewhere, and obviously, they already broke up.
Now tonight’s riddle was my very first Harry Potter riddle. It is actually about two ships.
Here are a couple of het ships
That would disrupt a favorite slash pair,
Though loyalty to the Phoenix
May be the one thing they all share.
I say this because of the women
My knowledge is dreadfully light;
I only know one is a martyr,
And the other resembles Snow White.
The first can be seen with her lover,
By his side in an old photograph.
Though they have long been divided,
They are now reunited at last.
The second must overlook much,
If she will with her lover abide.
Up to now we’ve not seen them together,
Except on Privet Drive.
Closed book, you might never get it, but open book I think it’ll be pretty easy.