Is it gum disease or not please help me?

hi im really worried about my gums i searched everywhere but i cant find an answer for my problem...s since i was 10 years old my gum have bee like falling from my tooth but just from one. the reaserches ive seen say that is caused by not flossing or brushing good and is a yellow tartar that eats the gum with time and this can leadto tooth loss too..but i brus and flos good and i dont have that nasty tartar on my teeth and th weird thing is that is only on one tooth ...i cant affort a specialist ar somthing like that so please just anything you know tell me. i really appreaciate it thanks help me please