How would you have hepatitis b if you have only had sex with one person and that person has only had sex with you and you or your partner have never done any drugs with needles or anything like that...

Plz help


is it something to be concerned about, I have read that low risk cases ( which 'most cases are) only last for about six months or it can only be contagious within those months..Something.. But it will always show up in your blood that you have been introduced to it before but you may not actually have it..