The Amulet of Silvanus - A Vampire Spawn's Donor's Best Friend | Baldur's Gate 3 

You can romance him without letting him feed on you after the first time. He agrees to stick to animals and people who are determined to die to the group if you don't express interest in being fed on anymore.

@Magpie5yndrome it's not so much about my tav not giving consent or wanting to avoid getting their blood drank, (apart from the debuff) it's more an issue of asterion hating my choices so much I'm going to need to be a donor for any chance of love

@@one_for_one You don't need to do everything he likes to romance him. I've done plenty of things he disliked and still got a romance with him. Installing a mod that shows approval was really eye-opening, actually. The biggest approval yields (+5, +10) come from trusting him, treating him kindly, and reinforcing that he has the right to consent. The rest of the stuff is +/-1. A bit of schadenfreude if you appeal to what he likes, eyeroll and a bit of annoyance if you don't. It's quite easy to get him to proposition you even before the tiefling or goblin party. From there, do what you can to help him and just be kind to him. He'll be making moon eyes behind your back in no time.

I believe Paladin's Lay On Hands can do it, too.