Worried about getting stds with this online thing?

I'm not looking for a relationship and I don't want to ask any of my girl friends (platonic, not romantic) if they want to expirament with me and I'm a virgin and my curiosity is getting really strong. Masturbating while it does satisfy me somewhat, just doesn't satisfy my curiosity fully. I'm 18, I plan to use a condom of course and ask her if she has any stds, but I know that they don't always work.. Blargh, as much as I'm looking for casual , my head is telling me its a bad idea.. thoughts? :|