Does conditioner damage hair?
No.
If a conditioner is damaging your hair, get rid of that conditioner. STAT!
Conditioner when used in excess (i.e. half a bottle) and left on for a long time (i.e. overnight) under a plastic cap can make your hair very soft almost mushy, but that should not cause damage to your hair.
Conditioner is like fertilizer to the hair. It helps your hair, not hurt it. Your hair should be fine when you apply conditioner and leave it on the hair for a hour under a plastic cap.
Make sure you rinse thoroughly.
Remember to experiment and find out what works for you. Soon you will be enjoying your lengthy hair goals.