The detachment part would have to be distinguished from that which is healthy. And that which is unhealthy.Healthy- when within the relationship, you unknowingly expect Aqua to take responsibility for your emotional state. Or you play emotional games when trying to get their attention.
Unhealthy- When they break off engagements unapologetically,expect you to be available whenever its convenient for them or go through long period of times without answering your calls nor respondibg to your messages.
The Aqua I am friends with also has Venus in Aqua squaring Pluto with Mercury, Moon and Mars trine it. He was pretty intense and my Sag nature couldn't stand it ;even feared him at some point. So he learned to tone it down a lot.
But i do understand that the Solar nature has the "detachment" most people find inaccessible. And his reasoning behind it is that he says he wants to mantain intellectual distance in order to better relate(the irony)
We are better friends in a crises(either his or mine). But there really wasn't much emotional expression between us until these recent years
His Asc in Cap forms an out of sign conjunction to my Sun. He dated a Pisces Sun with whom he fell inlove but there is a dramatic Cancer/Leo whom I would say is the love of his life.
It could be because of Dsc in Moon ruled Cancer(in his case), but I think that most Aqua fear getting attached emotionally because they often anticipate things changing and the subsequent disruption of that bond.
They don't want to seem dependent or "clingy" to others. But they may enjoy the emotional commitment on your side- perhaps even possessiveness too because it affirms to them that you care etc.
In a way it becomes a self-fulfilling prophecy when you break things off suddenly or make swift changes without involving them (because you believe them indifferent to the changes)
The truth is that they are affected by them and that it DOES hurt when you suddenly break off from them. But they are slow to acknowledge this- as they have learned to silence the emotional part of themselves for so long that it becomes repressed.