I used Gale in my party for the entire game, and he never died once.

Some or all of these things might help with protecting Gale:

1. Use Mage Armor on Gale at all times
2. If Mage Armor is not enough, use Mirror Image
3. Use Jump to get Gale into key positions where he can rain down magic but is hard to attack back
4. Keep Gale as far back away from enemies as possible, and after he casts his spell, move him even farther away
5. Get Gale out of vision cones after he casts his spell, and then Hide with bonus action