Let me start by saying that I've played the game since the EA, and have completed 4 full playthroughs at point and I've romanced Astarion on each of them. And, honestly, I cannot believe that it took me a whole 4 runs to realize that even though Astarion was supposed to be a PANSEXUAL, his story line paints a completely different picture.

Throughout the game as his story unfolds we learn more about his past. But one thing you will notice for sure is that there is not a single mentioning of any female in his past. NONE.

As a matter of fact what you see are all males :
   1. A darling boy, who he couldn't bring to Cas.
  2. Sebastián
  3. A handsome virgin from his dream (a line when you visit Kuo-toa)
  4. 3 out of 4 prisoners in the cage of Casadors palace are males (and the only female looks like a male, actually, until today I was sure that she was a male)

     Honestly, now with all the pieces in place in the released game, it seems that Astarion was not written to be romanced by a female character at all. And it's perfectly fine, not every character needs to be unlocked for everyone to romance. If that is the way they wanted him to be presented, maybe Larian should've locked Astarion to a specific romance path like Dorian from DAI.
     But Larian presented Astarion as a PANSEXUAL, that was their sales pitch to us female players (the overwhelming majority of his fan base are females). Well, Larian has made a claim but they have nothing to show for it. You'd think that a true pansexual would swing both ways, but Astarion's story shows a clear preference for males, in fact it shows that it is his ONLY preference...

The reason for my rant is not that Astarion is written the way that he is, but the fact that he was ADVERTISED to be something that IMHO he is NOT. I feel like I've been LIED to by the Larian's false premise of him being pansexual, when in reality there is NOTHING to make me believe that it is so... I've been sold a story of a guy, who is based on his personal arc has no business romancing a female, at least judging by what is presented in the game. I really feel cheated by Larian's half-truths prior to a full release. And I CANNOT believe that there isn't a s...t storm of complaints from the female base about it.

If Larian stands by that Astarion is a pansexual, then they should correct his story line and include at least ONE mentioning of a female romance added to his story line, so it doesn't look all one-sided. Maybe change his story from a "darling boy" to a "darling girl" and add another female to the cage. That would add some parity... Give us at least SOMETHING to make it seem PASSABLE that he is actually interested in females just as much as in males.

This is my personal opinion and conclusion after going through the game many times, hearing and seeing everything that is presented in the game. Your mileage may differ smile