what are the chances of catching something really nasty as a result of  daty

the chances of ending up as maimed and gimp from turning the ignition key and entering traffic in your car.

Small.

http://www.vpul.upenn.edu/ohe/library/Sexhealth/sti/riskchart.htm

http://www.health.com/health/condition-article/0,,20188674,00.html

Demographic studies say the risk is small for me. Lets say I was a male 16- 18 yr old having sex with females of the same age, my risk would be high. If I were in California it would be higher. If all of these factors were true and I were poor my risk would be highest.