The biggest problem is a person can look completely healthy and be HIV positive.
Lymph nodes can be swollen for hundreds of reasons.
Don’t have sex unless everyone has been tested. If you have sex before the test, make sure you use condoms, that includes oral sex.
The test can be a false negative if the person was recently infected, so it’s prudent to use condoms until you do a second test months later. If they aren’t being faithful you should never take the condom off.
Sex loses some of its fun with all the diseases you can get, and my bet is most people get something at least one time in their life. Sucks.