thank you for responding so promptly! but i'm still a bit troubled. basically the third part of the flow chart applies to me:
"there may be a LOW risk of pregnancy if semen is shared mouth-to-mouth between two partners, and then one of the partners performs unprotected cunnilingus (oral sex on a woman) with semen or traces of semen on or in his mouth."
i'm not that worried about STDs because my boyfriend and i have known each other for a long time and i am relatively confident that i don't need to be concerned about this at this point. but when can i be absolutely sure that i'm not pregnant because of this (eg. when i get my next period)? how will i be able to tell? is there any action that i can take to give myself a little more peace of mind? am i being too paranoid about this, considering that i'm only at a low risk of pregnancy?