How can you get it if your only sleeping with one person ? Does this means your partner is cheating ?

Update : We have been together for 6 years . There are no signs from neither of us . He went to get one and he don’t have it . I’m ordering a retest because there is no other explanation

Update : He does have it , he lied . He was my first and only . Never have I been with anyone else. We are no longer together because I don’t play about things like that .