Listen, I've seen a lot of fics a where Pure Vamilla Cookie is a virgin and Shmilk isn't, and thats fine and dandy in all, but like... look at these two.
Pure Vanilla Cookie has been traveling the world for a long, long time, and has been doing so for thousands of years, and he's met a lot of people during that time. Shadow Milk was literally made for a singular task and did that while in his little tower, his only friends being the other beasts (and we don't even know what their relationship was besides their convos together in battle), and my guy is so completely lonely and every Cookie he met, even before he was a beast, worshipped him as a god and probably thought he was completely untouchable bcuz of his power.
All I'm saying is that, if you want one of them to be a virgin, it makes way more since for the virgin to be Shmilk.