That is just not true. They have deep feelings and do love, but they don't show it physically. They do and can love each other, but their culture works differently than ours. The children are still raised by elders, just not their own birth parents. They do have a family with their peers and form relationships that are every bit as meaningful as any conventional family in Thedas. Sten had strong feelings of brotherhood with his other Quanri scouts that came with him, which is proven if you do his Fade sequence during Broken Circle.
For adults, you can have romantic love without sex. There is several asexual forum posters that have repeatedly said as such. Anyway, to address your question Doc, I really don't think it's an issue due to selective breeding. There might be Quanri that are attracted to men, but we're talking a culture that separates love and sex very thoroughly.
A feeling of brotherhood is not the same thing as romantic love. I played the fade with Sten and saw the scene you refer to, but that isn't romantic love. Also, the children aren't raised by elders, they are raised by what are basically women priests, but it isn't a parent child type of dynamic. It is like they are sent off to a private school at birth.
The qunari don't practice affection as others on Thedas do. Sten says as much. They don't truly even have a concept of personal identity or property. Sten isn't even sten's name, its his rank. "Stop teasing the Sten". Sure Sten has his sword, but he says it isn't a thing he owns but a part of his body.
So no, while we don't know, what we do know leads me to believe that Qunari practice a very duty and service life style and I do not expect that Qunari society allows for hetero or ****** sexual relationships outside of breeding purposes.