I'd like to say I'm not picky since those qualities seem so natural to me, however in this materialistic age it may be considered fairly high standards ...
Let's see, absolute monogamous mutual exclusivity and dependency are crucial. I despise the idea of some intruder receiving too much of my or my s/o's attention, with the exception of family members I suppose.
I've been saving myself sexually and I can't really imagine myself dating a non-virgin. I couldn't care less about the social status of it or anything, it's just that intercourse, while not mandatory, is like a sign to the contract of love to me. Dating someone who's gone that far with someone else before, no matter the context, simply ... feels wrong.
I'd also like to have my own kids someday, so despite me being panromantic, compatibility in that regard (I'm a guy so someone with XX chromosomes and fertile) is also highly appreciated. I think that box not being checked would be the easiest to cope with for me out of these.
Other than that, the obvious stuff – I'm not able to love someone who doesn't align with the values and beliefs most important to me (being a silly goofball for example ^^).
never ever let go, even if it hurts