@LT123- I had a feeling it was something like that. Bianca has something to do with a past love, maybe? Not that there's any way to tell, but that's my guess.
Bianca's codex entry:
Varric's crossbow is a marvel of dwarven craftsmanship, clearly the work of a master. However, she bears no smith's mark.
When asked how he procured the weapon, Varric has a few claims. He could have won it in a game of Wicked Grace against Paragon Branka, it could've been a gift from a mysterious old beggar who disappeared into thin air, and it's possible he bought it off a crooked merchant in Lowtown with the previous owner's hand still wrapped around the trigger.
None of those explanations is very likely and continued questioning simply results in Varric grinning and walking away.
It doesn't shed much light on the matter, unfortunately. Bianca will forever be a mystery~
By the way, have any of you had Sebastian and Varric in the same party at some point? but I came across this hilarious banter where Sebastian offered to give Varric a few pointers. Varric sounded very offended at how Sebastian even suggested touching Bianca's trigger LOL. xD