Why does my family ridicule me for this?

I don't like getting involved with girls very often because I don't have the heart to mislead them into thinking i want to be serious. I'm only 19 and usually when a girl likes me i turn them down because i know they want a boyfriend but i don't care about having a girlfriend at the moment. if i didn't turn them down then i would just be using them for sex. My family always ridicules me for never having a girlfriend. what do you think and what should i do?