Someone made a great point from that locked thread.
The game originally was going to make you stick to romancing the one partner you chose at the tiefling/goblin party. To quote an author: "This locked fans into dating the same character simply due to a few choices made toward the start of the game. As a fan before coming to work at Larian, though, Author wished players could experience love triangles and multiple partners." The freedom to do this sounds great except that left people who are loyal to Astarion with a lack of content. You're rewarded for romancing Shadowheart and Astarion at the same time up until the choice in act 2, because you get some cool romantic dialogue from Astarion when he reacts to you breaking up with Shadowheart, which you miss out on if you're loyal.
There is no reward for being loyal to your romance in BG3, which is a shame. Is this off topic? Not really, I think Shadowheart said it best, that Astarion is fragile when it comes to love. I think out of all the companions he is the least secure and needs the most reaffirmation of love from his partner. It's due to this insecurity that makes AA so keen on turning his lover ASAP so he can be sure they'll never leave him. Being loyal to Astarion should have positive effects down the road for both spawn Astarion and AA. Perhaps it allows for AA to be less controlling and allows spawn Astarion to seem more confident about your relationship in the epilogue.
