HPV is spread by skin to skin contact. The HPV you are referring to is the strains of HPV that affect the genitals (vagina, vulva, cervix, anus, rectum, penis, mouth/throat). There are two major types: low risk (warts) and high risk (which can lead to cancers).

If you have ever had any sexual contact (not just sexual intercourse) with anyone other than this partner, then it would be very difficult to determine who/how/when you were first exposed to HPV. HPV is not a good way to determine fidelity. It is possible that your partner has not been monogamous. It is also very possible that the virus has been in you for a period of time and it is just now being detected.