My husband has a lady friend, who I have labeled his "non-sexual partner". The two of them have labeled her his "sister". It's not romantic in any sense (probably more by her choice than my husbands), but there is a relationship there and an emotional attachment. Many people mistake them for husband and wife (until I show up
She takes my kids to the doctor, school activities, etc and when I can't make it to one of the kid's sporting events, she shows up with my husband (has the baseball and football mom's scratching their heads, especially when I look confused when they call her my sister in-law). She and her family are basically part of our family now. It took me a while to be comfortable around her, but I can now call her a friend.
I would say that a "non-sexual" partner goes beyond even close friendship.