You are not alone!
This is a very common problem among freestyle swimmers. Practice these drills to overcome this and improve your stroke:
1. Kick on your side with your arm extended. Belly button should be pointing directly at the wall, eyes at the bottom of the pool, hand extended. When you need air, roll onto your back and grab a few breaths before going back to head down.
2. Shark Fin Drill. Start as in #1. Lift your trailing elbow up, and drag your hand through the water until it gets close to your ear or goggle line (forming a “shark fin”). Slide the hand back along your side, roll up to get air and repeat.
3. 6 Kicks Per Stroke Freestyle. Swim freestyle but for each arm stroke, count 6 kicks. This keeps you on your side longer than usual. Make sure to keep your arm out in front as you do the 6 kicks.
These drills will help develop your ability to be balanced on your side and ultimately improve and correct your arm dropping as you take a stroke or take a breath!