There are several causes of leaf drop on azaleas but from the photo you sent I notice sandy soil, no mulch and an exposed location. The soil most likely dries out. I suggest you mulch with compost or bark chips and water in late summer and fall. Often a plant will bloom heavily when it is stressed as it thinks it will die soon and wants to leave seeds for the next generation. You may also consider moving this plant to a location where it gets only morning sun with plenty of organic matter mixed into the planting hole. It will appreciate the effort. Keep growing, Marianne Binetti