I don't want to break up with my girlfriend/stepsister
Why would you date your step sister?
I love her genuinely and I don't know what to do without her
You shouldn't date someone in your family. Other family members will find out and think you are weird.
She's my life and I can't live without her.
If you continued dating your step sister, you could be setting yourself up for a long bumpy road within your family and extended family. You should let her go and find someone outside of your family.