I've been running a little experiment with this romance based on the following questions:
- What would happen if you had Astarion in your party when speaking to Raphael at Last Light Inn (where he asks Raphael about the scars), but not have Astarion with you when Raphael appears outside Gauntlet of Shar?
- What happens if we find out the meaning of the scars through the Necromancy of Thay/Tharchiate Codex instead? Meaning we have to wait until Act 3 to fully unlock it.
The below followed:
- Upon meeting Raphael outside Gauntlet of Shar without Astarion, Raphael never promises to reveal the meaning of the scars if we kill the Orthon;
- I went to Astarion at camp and let him know I stumbled upon Raphael outside Gauntlet of Shar, which he bemoans not having been there for, but says that maybe we can still salvage this and have Raphael "owe us and be in his good graces" if we kill the Orthon for him;
- I take Astarion with me and talk the Orthon into killing himself;
- I never took Astarion to Araj Oblodra;
- I spoke with Withers with both Astarion and my PC, who mentioned the "bosom companion" line. This confirms the relationship is still on-going AFAIK.
- Raphael never appeared again for me in Act 2 and love confession scene never triggered.
Starting Act 3, that line "We haven't spent a night together in quite some time..." appears.
- If you pick it, breakup scene ensues. Quite a nasty one at that, well written Larian

I reloaded the save and avoided that dialogue option for a while.
I also avoided looking for his siblings, as they will tell him about the ritual and I wanted Astarion to find out via the Necromancy of Thay book instead.
- I got Astarion to unlock the Necromancy of Thay with the Tharchiate Codex where he mentions he found Cazador's Ritual and needs some time to process the information. Some long rests afterwards, he has nothing to say about it;
- We go to Cazador's Palace and stop the ritual with Astarion remaining a Vampire Spawn;
- After a long rest, he thanks me for helping him with Cazador;
- No graveyard love scene happens;
- I pick the option "We haven't spent a night together in quite some time..." - He breaks things off and even mentions how you failed to help him in return for his "excellent services".
This dialogue option also
does not go away afterwards.
And he keeps starting any dialogue with the same stuff he says as if you're in a relationship still. ("Hello, my sweet. Hello, beautiful", etc etc)
It feels like the romance is buggy at this point?