HPV is a horrible test for fidelity!
Someone can be exposed to HPV during his/her first sexual experience. It doesn't even have to be the first time one has sexual intercourse. HPV can be transmitted anytime there is skin to skin contact between the vulva, vagina, cervix, penis, anus/rectum, mouth/throat.
There are over 30 strains (of the over 100 total) that can negatively effect the genitals (those body parts that I just listed). Some of those cause genital warts (low risk HPV) and others can lead to cellular changes which could results in cancer (high risk HPV). It is possible to have more than one strain of HPV. Most people who have had sexual contact with more than one person at any point in his/her life is most likely exposed to, and possibly has HPV.
HPV can cause problems as soon as a few weeks from exposure up to several decades after exposure. Stress (like having a baby) can lower the body's immune system which can cause HPV to cause problems.
I hope that helps.