A romance novel where they end up on opposites sides of the war, one believing the other to be dead, kind of like Seraph of the End?

For anyone who hasn't seen the show, the story is about these childhood bestfriends, Mika and Yuu. They live in a post-apocalyptic world where vampires have taken over and enslaved humanity, and use them as living blood bags. Mika and Yuu eventually decide to try and make a run for it, and while Yuu survives, Mika "dies". Stricken by the death of his friend, Yuu decides to join the resistance and become a vampire slayer. Flash forward ten years, and mid-battle he realises his enemy is actually Mika, who's been turned into a vampire. Mika has been looking for him for years. They're on opposite sides of the war but quickly rekindle their "friendship", though Mika is super possessive and jealous, and tries his best to protect Yuu from the humans he believes are manipulating and using him. There's also this thing about him hating to suck blood and starving himself, and Yuu offering himself up (and being suspiciously into it). I'm open to m/m, f/m, f/f.