How dangerous is uti bacteria resistance? although i haven't blood in urine or pain or burning sensation my doctor thinks i have uti and put me on my second antibiotic prescription and i'am freaking out i may have bacterial resistance. is it fatal?

Alternate antibiotics usually work just as well as the first choice. Rarely serious and virtually never fatal, especially at your young age. However, profile says you are male age 21, in whom UTIs are rare. Is the diagnosis certain? Not urethritis (i.e. STD)? If true UTI and male, complications are common and you need CT scan or other imaging to check for potentially serious underlying reasons.