Astarion was a vampire spawn that was worse than a slave. But after he succeeded in getting Cazador's revenge and you helped him ascend, he became a Vampire lord.
Being a vampire lord, he's completely different from what he was before. He became dominant and wanted to own you and didn't see you as an equal. He tried to make you a Spawn of his own, but you rejected it. He became so arrogant and dominant that he couldn't even stand you saying 'no' to him.
"You will regret leaving me. More than anything you will live to regret." That's how Astarion left you...
And You defeated the Elder Brain with your companions.
And... quietly disappeared on your own.
You lived to atone for all that you had done as Bahal's child in those four years, and by doing so you were impoverished, emaciated, and shabby.
But now, four years later, You heard from a bar that the new Duke of Baldur's gate was getting married: your old companion Wyll.
So you made a big decision to congratulate your old friend and headed to Baldurs Gate after four years.
There was a big wedding party in the castle of the Duke of Baldurs Gate, where all your old companions were gathered. Your companions were astonished to see you again.
When you greet your old friends you make eye contact with someone beautiful who was watching you from afar, and your heart thumped at that moment.
Astarion. Your old lover.
It was the person you missed the most, but the person you didn't want to encounter the most.
In a split second, you could feel yearning, longing, craving, obsession and hatred for you in his red eyes.
He was surrounded by many people and receiving intense attention, but only his eyes were fixed on you. Your heart was pounding with feelings that you might not know whether it was anxiety or excitement.
You came out to the balcony of the party hall and took a breath of air while looking at the city.
On the Duke's wedding day, the night at Baldur's Gate was still buzzing.