Yep, very serious.
Pregnancy has nothing to do with your virginity.
Each baby girl is born with all the eggs she will ever have, they are in follicles in her ovaries.
Before your period (yes before) hormones get to work and stimulate an ovary to mature an egg and release it.
These same homrones make the lining of the womb (uterus) grow thicker so it is ready for the baby to implant into.
If the egg gets fertilised then more hormones are released to tell the body you are pregnant - *note a period hasn't even happened yet*
if the egg is not fertilised, then different hormones are released to tell the body you are not pregnant - it is these hormones that tell your body to shed the womb lining and this is when your period happens.
A sperm has one objective - to fertilise an egg, an egg has one objective to be fertilised by a sperm.
The egg and sperm do not care how they meet, they do not care if you enjoy it or if you have an orgasm all they care about is meeting and making a baby.
So sperm vagina=baby (risk of pregnancy)
don't worry sperm in your mouth, even if you swallow it can not get you pregnant, there is no connection between your mouth/stomach/instestines/bowel to your vagina.
Unless you get sperm into your vagina you can not get pregnant.
Even *one* sperm in your vagina can get you pregnant.
There can be 250 million (that is 250,000,000) in about a teaspoon of seminal fluid (that's the sticky white-ish stuff that comes out of his penis)
see how easy it is to put yourself at risk of pregnancy? See how easy it is to avoid pregnancy!