Hi Maxipad101!
It is good that you stopped once you were feeling uncomfortable! I think you are on the right track for dealing with that tear- if it isn't bleeding, you can continue to treat it gently until it heals. When you say you know that your partner doesn't have any STIs, is it because both of you have been getting regular checkups?
It's true that UTIs are not sexually transmitted, but you can still get a one as a side effect of sex - bacteria can be introduced to the urinary tract during sexual activity. Staying hydrated can't hurt, but you should consider seeing a doctor in case you need antibiotics. If I may ask, what would happen if you asked your parents to take you to a doctor?
Getting lube could really help with the dryness and friction that you've mentioned - spit can only do so much. You could buy it, but there are also organizations in your state that offer free condoms and lube. You can pick them up at many sexual health clinics, or you may be able to have a discreet package sent to you or your partner. These websites can help with the latter: