I'm considering to quit my orthodontic treatment after 8 months. what are the consequences ? is there any way to remove braces without pain ?

More info needed..: You don't say why you're considering stopping or how long your treatment is expected to take. Occlusal stability (how your bite currently presents) can be compromised, leading to tooth fractures, periodontal issues, and possibly tooth loss. Speak with your orthodontist about your concerns and seek a second opinion if you're not satisfied.

What a shame: To quit part way through treatment can lead to instability of your dentition, excessive wear and/or fractures of your teeth, damage to supporting gums/bone, and possible joint damage. Any Orthodontic Specialist can painlessly remove your braces, but early removal may be disastrous in the long run. Discuss your concerns with your treating Dentist or Orthodontic Specialist.

"Painless Removal": The prematurely termination of the orthodontic treatment could result: gum disease, cheek biting, compromised esthetics, not corrected malocclusion, possible TMJ disease, just to name a few. It is not recommended, but you have the right to do what you believe, is in the best for you.