What's the difference between a QPR and a romantic relationship?
A QPR is an intimate non-romantic (non-sexual) relationship. Essentially this makes it a very close friendship where the parties agree to be committed to each other in the long term (e.g. living arrangements, family assimilation, etc.); and that is celebrated by society in the ways that a regular relationship is, perhaps with ceremonies and legal codes such as marriage, anniversaries, etc.
The key distinguishing difference between a QPR and a romantic relationship is that a QPR lack elements of romantic love. Romantic love may be considered to include "butterflies", a loss of appetite, an increased heart-rate, or even a feeling like the love can transcend space and time.
At the end of the day there isn't a hard delimitation between QPRs and romantic relationships. An alternative way of thinking about QPRs is to say that they're about looking at the relationship 'from the other direction'. Calling a relationship a QPR can be a convenient way of working from a different set of assumptions than the standard romantic ones.