My tooth all the way in the back is broke in half all the way to the gum line. What can I do about it? I'm so scared

speak to a reputable dentist about your options.if the tooth needs a root canal and periodontal crownlengthening to get it perfect then you may prefer tohave it removed and a implant placed.  Teeth restoredby implants have a very high success rate and mostpeople agree that the procedure is not so bad.A tiny chip sometimes feels like the grand canyon in your mouth.It may not be as bad as you think.  I would go see your dentist right away.

You don't mention if the tooth is broken horizontally or vertically. If the fracture is horizontal it may be possible to do a root canal and build the tooth up then do a crown. If the fracture is vertical removal of the tooth and an implant is the best option.  Visit with your dentist about your options. Allow them to take some x-rays and do a complete exam to get an ideal diagnosis.