from diffusers import AutoPipelineForText2Image
import torch

pipeline = AutoPipelineForText2Image.from_pretrained('black-forest-labs/FLUX.1-dev', torch_dtype=torch.bfloat16).to('cuda')
pipeline.load_lora_weights('busetolunay/background', weight_name='background_3.safetensors')
image = pipeline('[trigger] style, A stone-paved courtyard surrounded by tall brick walls. In the center is a large fountain with water flowing down in layers. To the left, there is a bench under an old oak tree, casting long shadows on the ground. The sunlight is breaking through the branches, illuminating patches of the cobblestone path. A few birds are perched on the fountain's edge.').images[0]
image.save("my_image.png")

For more details, including weighting, merging and fusing LoRAs, check the documentation on loading LoRAs in diffusers