If you are concerned, there is no harm in getting tested. That being said, it is almost impossible to catch HIV or AIDS without sharing blood (through needles, transfusions or sex) or sexual fluids.
You can not acquire HIV from sharing bottled watered or food with an infected person. While it is true HIV is transmitted through bodily fluid it does not get transmitted through saliva. The only way that you could be infected would be through sexual contact with your friend, tainted blood transfusions or if you shared a drug needle.
There a very, very slight possibility that HIV could be transmitted through spit. There has never been a single case of it actually being transmitted that way, but there is technically a chance that it could happen. It is estimated that you would have to drink around 12 gallons of spit for it to be an issue.
Testing has been done for many years, and HIV and AIDS is not transmitter by food and drink. It is spread through blood and bodily fluids. Having unprotected sex with your friend, or any person can spread these diseases. Coming into contact with a cut, if you have an open sore is also possible.
I do think that you can be at risk because you are swapping germs when you share drinks and stuff. It would be like kissing them with a open cut in their mouth.