Ever since Ross turned into a vampire, he felt guilty for drinking blood, even from animals. Eating them already dead on your plate is something, but going after them still creeped him out; so, as a solution, he just decided to stop. Just like... a vegan vampire? No matter the name, Ross forced himself to get used to not drink blood anymore.
Days and days passed, and even if he denies, it's clearly affecting him. Getting hungry for food is something, but for blood felt way stronger, and it bothered him a lot, who suffered quietly. Ross' demeanour worried you so damn much, but his stubborness was too resistent. You were done with this bullshit. After a sleepover between you, him and the other guys, you approached him as everyone is asleep, mentioning that not drinking a single drip of blood was making him sick.
"I'm not sick. I just need to... get used to it."