In ye olden days (EA) this was the order the sequence followed, (it might have changed, I did notice some changes in the way scenes triggered but I didn't make note of it so it's possible):
1. There's a long rest where you see Astarion sneaking away
2. Now the boar's corpse is there
3. Inspect it, Astarion intervenes
4. Long rest and bite night ensues
It definitely didn't trigger if you didn't run by the boar back then, I remember my frustration at how low my approval was by the time of the party back then because of this.
As far as I remember, that's the order now. I usually rest a few times so I don't miss all the scenes and dialog. In the following order:
1. Found the companions and Astarion (a party of 4 characters) - rest: scene with Gale and the campfire, Astarion wonders are we staying here? (If you approach Astarion last on the first long vacation. He won't want to talk)))
2. Going through the ruins and picking up Laezel - rest. Scene knife, rope or poison? Astarion must go into the forest.
3. I run through the battle at the gate and run to the bridge to find a boar - rest: Bite.
4. Go into the grove with Laezel and go to Zorr, talk to him - rest: Stars.
I return to the grove, go around it.
But, if you cross the bridge before these scenes, you can lose the scene with the stars or the choice of knife, rope or poison. Further in free order, the scenes are not replaced and fall out normally.
If you engage at the gate before Astarion goes into the woods, the boar's corpse will be lying at the other end of the bridge, or not far, from the lair at all owlbear.
If you play as Urge, he pushes the scenes back by himself, (bedtime thoughts - first night, bard - if you find her in the grove, she will appear at the first long rest when you cross the bridge, butler - next long night)
When you find the lair of the owlbear, (after the battle or after finding the lair, I don't remember exactly) triggers the scene: I drank the bear.
If you find a book in an abandoned village and give it to Astarion, the scene with the book will start in the evening.
