Thanks for all the advice!
Well, my fiance and I have decided to call off our engagement and part ways amicably so it looks like I won't be a SM after all. Quite honestly I'm pretty relieved to be relinquishing the step parent role.
I wanted to reach out to the forum though and thank all of you that provided honest feedback rather than sugar coating the realities of living in a blended family. Through all of the difficult thoughts and feelings I have struggled with over the past year and a half, I have felt so grateful to have found a group of people out there that has been through it too and is willing to share.
Having previously been in serious relationships where children (current or future) were not a consideration, I realized the unique and difficult challenges that come with kids - especially when they aren't yours! I'm hoping to perhaps someday find that perfect guy with no kids so I can stay away from this forum. :)
Thanks so much for all of the help everyone and best of luck in all of your families.