I am a step parent to two children and I love them and my husband very much. I just really like to hear from others in my position about the challenges you face, especially when dealing with the birth parent that is not in the relationship.
I'm not in your exact position, just the other way around. I'm seventeen and my parents divorced when I was seven, so I'm quite used to it. My dad dated a girl on and off for about five years and they finally got married. It can be a stressful and awkward situation. At the end of the day nobody could ever take the place of my (birth) mom, she comes before my stepmom in my eyes. Don't get me wrong, I love my stepmom too! I'd have to say it takes a lot of communication to figure it all out, it won't come overnight. I made a solid and good relationship with my stepmom by talking to her, and also spending one-on-one time with her, whether it was lunch or running errands it gave time time for us to bond and connect. Discipline was never really an issue, as I'm pretty well-behaved but she definitely had to break up some arguments between my siblings and I, but if anything more serious came up my stepmom knew her boundaries and let my dad handle the situation. Overall my stepmom and I built a good relationship, by talking with one another often, spending time as a family and by doing things we both enjoyed, it definitely didn't happen overnight, but it did eventually and I know she's always there for me! Hope this helps!