ive been losing weight 70 pounds in fact i want to quit smoking but ive heard i could gain like 20 pounds back i exersise 6 times a week and can watch my diet very well if i quit will it send me backward in my weight loss goal or if i stick to my diet and exersise plan can it stop me from gaining weight back

People gain weight when quitting smoking because they crave the cigarettes and rather than smoke they eat something instead.
So it’s snacking that will make you gain weight, not the actual act of quitting smoking.

Quit smoking, and just keep an eye on what you’re eating…
Good luck