i get these tears at "6-oclock" or the perenium area - as well. For some reason, that area has just become very sensitive to me - even going to the b-room (sorry tmi) can cause it -- so it sounds like you were under lubricated perhaps... BUT if you're really nervous, or unsure, the best thing to do is get checked.
Well you should be worried about contracting genital herpes as you are not protected by the condom and you have a ripe and ready entry point. The "tear" is likely from being under-lubricated (as well as the soreness).
I wouldn't be worried about STD's really. I think it's more of your body not being completly prepared/too fast or hard/fear...Believe me..tons of reasons.