many people with hepb live pretty long as long they keep monitoring it every 3 or 6 months, this is treatable. You should go get vaccinated if you have not do so. If you love him I don't think there will be any doubt about staying with him. You never know, he couldda hit by a car tomorrow and die from it. You should talk to him about it and get to know more about hep b and ask him what does he have to go thru everyday.
In my country people who don't treat hep b can live until 60s or 70s. If they receive treatment maybe they can live longer.
you need vaccine and hbsab antibodies higher than 10miu/ml if you don t want to share hbv
once you know you have hbv you can check if it makes damage and in that case stop it, the problem of hbv is that like hcv is a silent killer, most are not aware they have it and after 20 or more years dye of cirrhosis or cancer knowing they have hbv when they are dying