If you feel a pain in your back when lifting your leg into arabesque, it's possible the issue is a combination of decreased flexibility in the hip flexors with weakness or restrictions at the spine.
You'll want to check the range of your hip flexors. When your quadriceps and iliopsoas are tight, they restrict the height of your arabesque. The more flexible they are, the higher you can take your leg before tipping the pelvis and creating the necessary arch in the lower back. Try doing your arabesque on both legs, then stretch both the quads and your deeper psoas muscle and repeat the arabesques. Did your leg go higher? If it did, it's a sign that the hip flexors are negatively influencing your arabesque height. If there was no difference, there may be weakness in the upper back that needs to be addressed.
Try lying face down on your bed with your upper body hanging over the edge. Lace your hands behind your head as you slowly lift your upper back to a horizontal position. Keep your abdominals engaged throughout the exercise and move smoothly, lengthening the spine as you lift. Do this 5 to 10 times, feeling the effort between your shoulder blades. This will begin to strengthen the extensors of your upper back that are essential for keeping the torso long and tall during arabesque.
Always make sure to allow the upper spine to rotate in the opposite direction from the rotation of the leg in arabesque. (You might think of wringing a washcloth.) Lastly, when you feel pain in the lower back, change your position. Pain is always an indicator that something is not right, and we all need to listen to our body's messages.