But ultimately it feels forced because like I said, all at once. If Shadowheart maybe wanted to meet alone to share her secret, and have a romantic interlude, Astarion maybe tried to tease if you let him bite you, little moments of romance throughout, that would make more sense.
I'm pretty sure that's how it is. Shadowhearts wants to meet alone, but specifically she does so to bond, just the two of you.
During Astarions scene, I had the option to offer him my neck or trust him not to bite me.