Human papilloma virus (HPV) can be present without symptoms for many years. During those years, it might not be visible on the skin. In women, it might not cause an abnormal Pap smear.
So either you or your partner may have gotten the infection in a past relationship. It surely does NOT imply that either of you have had sex with someone else since your relationship began.
Why might it show up after many years? There could be changes in a persons immune system that allow the virus to become active again.