You will never know. Could have been a lover from ten years ago. There is no way to play detective with this virus.
I'm not sure on the detective part. It's possible to play detective or at least be suspicious, based of course, on circumstances.
Scenario: 10 year monogamous relationship. female partner tests positive for low strain hpv over 3 years ago on pap. No warts. Virus clears. Fast forward to today, gets annual pap, tests positive for hpv again... with a different strain... says high risk. Isn't the likely source pointing to infidelity within that 10 year period? Otherwise, the strain should have tested positive 3 years ago as well. Correct?