here's how I deal with Gale's romance routine. Hope this will help you.
These are the important encounters (all in the grove) that can grant Gale's approval to the next level:
1. stand in front of the crossbow and pass the persuasion/intimidation check to protect goblin Sazza from getting killed.
2. save Arabella from Kagha successfully.
3. let Nettie poisons you and convince her to give you the antidote.
4. save the tiefling child from harpies.
there are other two encounters that do not give approval breakthrough but are still required:
1. rescue Lae'zel from the cage without violence
2. use persuasion check to end the feud between Zevlor and Aradin.
5 Gale scenes mark the progress of his approval. you need to trigger them in a long rest every time you get an approval upgrade:
1."go to hell" scene
2. mirror image scene
3. artifact requirement scene
4. the weave scene
5. lost Mystra scene
Here's a detailed walkthrough explanation:
After recruit Gale into your party, rescue Laz'zel peacefully as described above(the deception check seems to be the only one). have 2 long rests before entering the druid grove gate (you can have your second one after the gate fight). You should be able to trigger the "go to hell" scene and mirror image scene. Make sure Aradin survives the gate fight.
Enter the grove and solve the feud between Aradin and Zevlor. Don's do your second long rest after entering the grove bc once you enter the gate, the Sazza scene will trigger. After you come back, Sazza will be killed.
After ending the feud at the gate, go to Sazza's prison and do what has been mentioned above. Now you should be getting "medium" approval from Gale. long rest, trigger the artifact requirement scene.
You may recruit Wyll after the artifact requirement scene. I don't recommend doing it before the scene.
Go to the ritual site, trigger Arabella's parent's scene. you don't need to talk to them to trigger the quest. Just go to the chamber and save Arabella. Now you should get "high" approval from Gale. (PS: take Wyll and Shadowheart with you so you can get 2 inspiration points in one quest.
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Now you probably need 4 extra long rest to get the Weave scene. In my playthrough, Astarian has 1 special talk with you, Lae'zel has 1 conversation, Wyll has 2 special conversations. Then the Weave scene should trigger.
After the Weave scene, pick one of the encounters I mentioned above, you should get "extremely high" approval. long rest, you should get the "lost Mystra" scene.
tips & advice
1. you need to do your long rest after each level of approval to trigger the scene in order. If you miss one, you won't trigger the rest scenes afterwards. So don't do anything that can get Gale's approval before you trigger the current approval scene. (recruit Wyll can give approval to Gale but that one does not mess up the routine).
2. Giving artifacts to Gale will grant huge approval to him, which will mess up the routine. Therefore, no need to give him artifacts. You can get all you need in the grove like what I mentioned above. After the "lost Mystra" scene, you can give him artifacts freely or do anything he approves to make our lovely wizard happy
. BTW don't let him get close to Silvanus idol before finishing the routine. Otherwise, you will waste one long rest of him talking about the idol.
3.The minicamp is added in patch 5 so I don't know if Gale's scenes trigger well in minicamps. I did the weave scene and scenes before in the wildness camp. The "lost Mystra" scene can trigger no matter where you do your long rest.
Hope this will help you get what you want from our lovely wizard Gale. If you have other questions, I'd like to answer them.