Was on the same boat a few months ago and been through a lot... You should have told your GF as soon as possible... If you 2 were sexually active already have her checked ASAP by the ff tests
1. HBSAG - reactive (yes, infected)/ non-reactive (no, not infected)
2. ANTI-HBSAG- reactive (immune)/ non-reactive (not-immune)
My GF and me we're kissing for months already, we also had oral sex few (we plan to have our 1st penetrative sex on our upcoming out of country vacation hehe) times before I told her, but every time we did it my guilty conscience is killing me so I finally told her. Anxiety and fear engulfed her... There was even a time where she wouldnt even hold my hand nor kiss me... It was painful that your loved one is disgusted with you but I can do nothing but explain. I brought her to a doctor to ease her fears, good thing she listened.
I got her tested twice with a few weeks of spacing 2 months after our 1st oral sex and she yielded negative. She just got her 1st shot of vaccine and waiting for her 2nd shot in a few weeks.
Your level of infectivity also depends on many factors like HBEAG and HBVDNA count, if you are HBEAG positive it means that you are highly infectious. Just have her tested, 95% of the time, when an adult gets exposed to HEPB the person will clear the virus in 6 months.
Even though there is 95% chance she will clear it the problem here is gaining her trust back, if you know it long ago already and you've put her in harms way, then that's something else. If you only got to know it recently, it's educating her and letting her know that with proper lifestyle changes and monitoring you can live a (quite) normal life.
sex and blood the only way to transmit but again in adults it has no reasons to worry
mother to child at birth, in this case hbv gets cronic 95% times without vaccine
all the other ways to spread are useless because the virus is cleared 95% times without any symptoms or damage
the countries with mandatory hbv vaccine at birth (cuba, italy, singapore..) have eradicated hbv in about 10-20 years, this also eradicates most of liver cancer cases
hav is also a benign infection and hcv is only spread by heathcare settings, dentists, blood transfusions, so only hbv remains the most spread in those countries without vaccine