Looking for some guidance on how True Love is to be played, when one (or both) of the two true lovers is afflicted by the Gift.
Is True Love so blind that the social influence of the Gift is ignored, or does paranoia and love go hand in hand? Perhaps leading to humorous romantic misunderstandings (which sounds like a Flaw, not a Virtue)
True Love is a charism/gift of the Divine and as such magic affects it weirdly.
I would say a player took the virtue, so they get the result is says, Gift or Curse otherwise. i.e. Beauty and the Beast.
I totally agree with both answers so far, but let me add that the Gift is a general effect; it affects everyone. True love is an individual bond, it affects the relationship between two individuals. It is a good principle that the special case is allowed to override the general rule.
That's the gaming justification. Timothy gave the narrative justification.
The best in-game justification is on ArM5 p.75:
People do not get used to The Gift, even if they have lived with magi all their lives. They can, however, get used to individuals with The Gift, just as long association overrides the effects of reputation.
Unless a troupe sets up a verrry strange situation, one's True Love is used to one's Gift.
It is not «verrry» strange to be separated from one's True Love by ill fate. True Love is a rare Gift which does not necessarily depend on being together. The Gift may of course be given only when the two have grown together, but it would not be «verrry strenge» to see it given at the moment they met (or indeed earlier). Not in a medieval tale of romance anyway.
Given that both are supernatural Gifts, there is nothing to say that the Gift of True Love cannot override the Gift of Magic, particularly if the Gift of True Love is Divine, which I am inclined to say that it is, but even if it is Fay or Magic, or even infernal, there is no reason why it could not override a very general supernatural effect.
Yep. But it is verrry strange to never have learned to know each other.
Getting to know each other doesn't mitigate the effects of the gift. Being around each other for a long time does.
fair enough, which brings us back to the supernaturality of True Love. They just know each other. In fact, they have not learned to know each other, they just know by virtue of True Love.
So maybe the True loves simply have been together always in a metaphysical sense, whether or not they have met on Earth.
It seems that we can turn this around indefinitely, but whichever way we look at it, it is always the supernaturality of True Love that allows it to override the effect of the Gift.
Learning to know your True Love takes some time.
But as it will typically be far more intense than getting to know just about any other people, it should also take less time to get acquainted to her Gift.
If we are going with in game justification, ArM5 p.76 defines what established relationship looks like for someone with the Gift, or the Blatant Gift:
An Inn
Gift: He [the innkeeper] tries to make small talk with the magus, but clearly prefers talking to the companions.
Blatant Gift: while he is polite to the magus, he clearly tries to have as little to do with him as possible.
This does not look like what I'd expect from someone with True Love.
It's not blind. It's quite the opposite, it sees better. Everyone misjudges your loved one, but you can go past that (even if your loved one does look a bit weird sometimes).
This "established relationship" with an inn or monastery does not cover, how an individual used to a specific person with the Gift behaves towards them, namely (p.75):
react to them as appropriate to their actual behavior.
So no more effect of the Gift, unless the individual needs to anticipate the reaction of other bystanders.
Well, can True Love be 5 minutes old?
Because it seems to me that it should block the effects of The Gift from the get go, the same way that Parma Magica does.
Unless True Love takes a long time to grow, but then I wonder why would the other half stay around except through Stockholm Syndrome.
Take a look at Apprentices p.21f The Gift Revealed: even a youngster later manifesting the Blatant Gift can have a childhood sweetheart not affected to the least and becoming a faithful and loving True Love to them. Looks like there is a story ...
Every argument has a premise that has not yet been asserted. Is True Love something to become, or just something that is.
Personally, I lean on the trope of the couple that are just meant for each other, and the feeling that they have always know each other. This probably implies that True Love is part of the essential nature and something eternal which does not grow or diminish. It is or it isn't and will never become anything else. The Love that grows is to me the normal, subtrue love. YSMV.
Is there a canon or historical reference to resolve the premise one way or another?
That doesn't answer the point I made.
You're saying: True Love works when it happens before The Gift.
I'm asking: can True Love happen after The Gift.
True Love can be a Virtue or a Flaw. Finding ways to get them for a character is a task for the troupe and the SG, not for the rule book.
Yes, True Love can happen after the Gift, of course: there are lots of ways for it.
Just for an example plausible in most sagas, the Blatantly Gifted mage's sweetheart can also be Blatantly Gifted, both are Hermetic mages and use the Parma. They met at the Tribunal and bang! They are busy showing each other their collections of toads ever after. "Just don't forget your Parma tomorrow morning, sweetheart! I want to show you something ... 
"
A SG isn't exactly obliged to provide a Blatantly Gifted Disciple of the Worm with Wednesday Addams as the True Love, though.
Such things are a matter of judgement and taste, not of rules.
That's running around the issue.
Let's take a concrete example, just to avoid further misunderstandings:
Can True Love manifest itself at the first meeting between a troubadour and a Blatant maga?
Yes, absolutely.
Why not?
Love at first sight is a classic trope, be the love True or not.
As is love that starts as acquaintance, grows into friendship, and finally into love.