Cavity or gumboil?

Anyways, I wasn't allowed to go to the dentist for like 3 years now ._. I still brushed my teeth twice a day(brushing after a meal is not reccomended, food effects happen after 30 minutes of eating)

Still, I have a tooth that's about to fall off. I thought my dentist would get mad at me (lol) until I looked up "Will a dentist get mad at me"

Anyways, I feel a minor split on my tooth that's about to fall off.

Do you think its the effects of gumboil spreading, or a cavity from candy I ate last Easter , I barely ate any candy in Halloween?

If you don't know what gumboil is, look it up.