your biological mother has given you life. and that right there is a great thing. you also have to think about is our parents is trying to protect you from what might hurt you in the end.
i hear alot about women in your situation feeling empty b/c they want to know about there biological parents.
you should talk about how you feel, be careful with how you say it b/c it could hurt your step mom b/c she did raise you.
i was raised in a physical & mental abusive situation by my dad. and not to be insensitive, but if wouldve been better if he was an absent parent b/c he caused so much hurt to my mom, my 3 siblings, and myself. and this caused problems in our childhood, adulthood, relationships, and how we parent.
so one thing that you should be very thankful for is being in a loving family, and that is something that i wished i had.