As a currently-childless stepmom to 3 little boys (2, 4, and 6 when DH and I first met), you are asking all the right questions and have all the right emotions.
The truth of the matter is, there are plenty of people out there for you to be with who don't have 3 small children, and who don't have the drama of a high-conflict bio-mom in their lives. If you truly want to be childfree, then being a stepmom is the worst of both worlds. You don't get the freedom that comes with a childfree life, and you also don't get to raise children the way you want to. And a life revolving around raising children WILL be the biggest thing on your plate for the next 10-15 years of your life, even when they're not yours.
The only way it works is if you have a SO that is truly worth it. One who understands everything you're sacrificing to be with him, and one who doesn't balk IN THE SLIGHTEST at you saying things like "I don't want to be at home when the kids are at home" or "I don't want to do their laundry."
I chose this life because I love kids, I understand childhood development, I'm interested in the process of raising children, and because my DH is the perfect man for me. When I was at the point you're at in our relationship, I was devouring books to figure out if I would hate this life or if I could handle it.
These are my recommended books for you to read!
Dating the Divorced Man: https://www.amazon.com/Dating-Divorced-Man-Through-Baggage-ebook/dp/B00JBMM3DK
Stepmonster: https://www.amazon.com/Stepmonster-Look-Real-Stepmothers-Think-ebook/dp/B003WJQ64K
A Career Girl's Guide to Being a Stepmom: https://www.amazon.com/Career-Girls-Guide-Becoming-Stepmom-ebook/dp/B000QUCO1M
I(56M) just finished reading "Dating the Divorced Man" by Christie Hartman (https://www.amazon.com/dp/B00JBMM3DK/ref=cm_sw_em_r_mt_dp_xpp1FbXVKM8C1)
I highly recommend this book for you. She is a blunt and no-nonsense writer and the book is aimed directly at situations like you are experiencing.
I read it in an effort to understand my own issues and to try to improve myself/my situation if I could.