How to organize resources loading and unloading?

Hello guys. I have 340 sprites and I want to show them like a comic book. The comic book has 39 chapters and each chapter has around 6-10 pictures.

I noticed that Unity does not allow to loading resources from Resources folder if the file resources.assets is bigger than 2Gb, so I split all resources in two sets: first set of images are left in Resources folder, and the second set is combined into AssetBundle.

So now if I want to watch the first chapter it loads pictures from the first chapter, and if I go ahead and select the second chapter, it unloads images from the first chapter and loads images from the second chapter. But if I want to see the first chapter again then there are two situations.

1. If images from first chapter were loading from Resources folder - all right, it just loads them again.

2. If images were loading from AssetBundle - it can't just load these images again because when I was switching from first chapter to second, it unloaded resources from first chapter and they have been deleted now.

So how do I fix the second situation with AssetBundle and deleted resources? I just can't hold all unused resources in memorythe whole time.