I don't think they ever broke up tbh. For whatever reason she couldn't escape, so I doubt they had the chance to end things even if they'd wanted to. Either way, one of the devs (I forget which... possibly Varric's writer) said that we may get to find out what happened from Bianca herself so if the options there I'm gonna get them back together.
Yeah, I definitely want to know what happened from Bianca-- I've seen people brush her aside when talking about the issue, as though the only opinion on the relationship that matters is Varric's. It definitely depends on what happened, how they feel, and the details whether or not my Inquisitor will be for the two or 'this is sounding pretty awk and unhealthy, I'm outsie.' 
To be honest, though, while I do adore Varric and will have at least one Inquisitor for him if he's an option because I want to try out all the things, he definitely won't be my 'go to' romance. I've had enough of romances with past loves involved, especially when it's the source of the friction in the romance plot.