SO earlier today there was a debate on whether or not Solas could have had a relationship with Wisdom spirit, and I found it extremely insensitive that the only "real" relationship is if Solas pursued a mortal one. I'm not going to name names, but I'm getting a strong selfish impression that some people believe the only girl Solas could possibly go for is the inquisitor.
I find quite hard to believe Solas can have a relationship with a spirit. Spirits are quite sensible to how people perceive them, and are embodiment of a single quality. Probably experience-going to feel something outside their prefissed quality, would probably tranform them into a deamon. Like Solas say in his personal quest, a spirit who find itself taken away from its purpouse, became a deamon, because can't really cope with something different from its purpouse.
It's the motive spirits rarely survive with their nature intact when meeting a mortal.
Even Justice end up becaming vengeance because he was influenced byt Anders. When in Kristoff's body, he didn't had so many trouble because Kristoff was...well, dead. Justice have his memories to see, but wasn't influenced by his emotions, since where only ecoes.
Cole is an eception. He have a layer of complexity highter than others spirits because he have, somehow, survived in this world learning to cope with a more human life. Probably he made it because he thought he was actualy a human for most of the time. But his purpouse is still the one of compassion. He doesn't feel any desire different from helping people, he have less of this need only if he became more human like.
Beside all that, this is mostly my sceptic thought, I am sure Solas had past relationships, and just stumbled on a elven girl with a glowing hand that actually ended up becaming much more interesting and important to him that he thought. (and one with a fine booty, that doesn't hurt. Solas may like spirits, but is still a man. Too bad spirits can have sexy booty only if you want them to, and doing so they can became deamons.)