I'm demisexual, so hopefully I can help :)
Is is possible to be demisexual but grey-romantic?
Absolutely! You're sexual and romantic orientations exist on different spectrums, so they don't always match up.
And because if it is possible, would that make me amid?
If you like that term, then yes, since both your romantic and sexual orientations would be on a-spectrums.
What is tertiary attraction? The list I was given and a lot of different websites explained it differently and it doesn't make sense to me.
A tertiary attraction can be any type of attraction that's not romantic or sexual. For example, if I'm attracted to someone for their intelligence or aesthetics, those are both considered tertiary attractions. It might've been confusing since everyone experiences attraction differently and there are loads of different attracting forces that some people notice and others don't.
Would it be contradictory to say you are demisexual but also sex averse?
So, being demisexual is like being asexual until you're not. Demisexuals will not experience any sexual attraction until someone (or someones) comes along that they form a close emotional attachment with and, if the conditions are right, it's like a switch flips and that demisexual- who previously wasn't experiencing any sexual attraction to anyone- is now feeling sexual attraction to this one person (or specific group of individuals). This does not mean that every person a demisexual makes friends with will be the subject of their sexual attraction- it's just that emotional attachment and familiarity is the prerequisite to feeling sexual attraction in the first place.
I am both demisexual and sex averse. When I think about sex in general, it grosses me out and is not my jam. It doesn't sound fun or look exciting. However, when I'm not in asexual mode- when there is that someone who flipped the switch- I am not sex averse towards them. But they are they exception.
There are other demisexuals who are sex averse full time, no exceptions. Being demi has to do with what you feel, while sex aversion is what you do with those feelings- or what you don't. So there are demisexuals who are feeling sexual attraction, but don't like the idea of sex and don't plan on having it.
So no, it's not contradictory. However, sex aversity paired with demisexuality can manifest in lots of different ways.
Also, what are QPR's?
I really like Merry Squidmas's description. It stands for Queer Platonic Relationship, which means the relationship is founded on platonic feelings but it's queer in the sense that the people in the QPR don't follow typical friendship dynamics. They might be more touchy or lovey than normal best friends, for example. QPRs are so popular in the ace/aro communities because they are considered long term, commited relationships that aren't founded on sex or romance (though aren't exclusionary of sex or romance either). So, while some ace/aros may never be interested in that perfect romantic partner who's great in bed, they have a QPR which fulfills the role of life-partner/bosom pal, whatever you'd call it.