I wanted what was best for you.
I used to really love the first romance scene with Astarion (and I still do) but it hits so much harder after you know why he's doing it. That he's purposefully seducing you for protection and blood, that he's forcing himself to sleep with you, and this is a mask he's wearing.
It's a sexy scene and really feeds into the vampy (pun intended) jump-your-bones version of him you get at the start of the game. The whole thing starts out with him being so confident and suave, saying that he's wanted you ever since he set eyes on you and how you want to be known and tasted. It's like everyone's perfect vampire romance novel.
He's laying out the bait that's worked thousands of times over and luring you in. And you can just get right to the kissing if you want.
But, you can also stop and ask him, "And what do you want?"
And for just a moment the mask drops. This is not the same cocky seductive face we've had up until now. This is vulnerability showing. When has anyone asked him what he wants? When has anyone cared? Does he even know the answer to that question?
So he pivots. The mask snaps back into place immediately. He turns back into the master seducer and feeds you a line about shared ecstasy to get you back on track.
And then comes what is, to me, the pivotal moment. He asks you "That's what you want, isn't it? To lose yourself in me?"