Hi there Libelula,
I don't usually reply to posts, but it was so refreshing to see yours! Like you say there are so many nightmare step-parenting threads out there, which don't resonate at all with my experience of being a step parent. The one time I raised my head above the mumsnet parapet about my family set up I was shouted down that being a step parent isn't being a "proper" parent!
Maybe I was just unbelievably lucky but blending life with my husband and daughter has, for the most part, gone really smoothly and happily. Note that I refer to my daughter, not my step-daughter. Although she is my step-daughter I don't believe I love her any less than if I had adopted a child, and I wouldn't always refer to them as my adopted-daughter so don't constantly refer to her as my step-daughter.
My husband and his ex separated when she was small, around 18 months, and have 50/50 custody - with her spending alternate weeks at each house. They've always lived fairly close to each other (maximum about 15 minutes, which is where we are currently) so easy for school, activities, friends, and helping each other out with the odd last minute child care emergencies. Their relationship is cordial for their daughter, but definitely no love lost between the pair of them.
We met when she was 6 and her dad and I were friends for a couple of years before romance blossomed. We've now been together six years, and married for two.
I think it has helped that there was no sense of "replacing" her mum, as she has no conscious memory of a time when her parents were together, and that I knew her as a friend before starting a relationship with her dad, but I can honestly say being a family with her and her dad has bought so much joy to my life.
Her dad and I discussed how we would work as a family and both agreed that if we were serious about building a future together I should be an equal parent in our household. It wasn't just us getting together, it was us coming together as a family of three.
Although I don't currently have any legal parental responsibility we share all the parenting duties in our family - both the fun stuff and the discipline! Interestingly when my husband had a health scare earlier this year our daughter asked what would happen to her if dad died. We asked what she would want, and she told us that she would want to carry on living half at her mums and half at our home with me. Thankfully my husband is now in good health again but we are discussing this with her mum and making sure the legal framework is in place to ensure her wishes would be followed.
I think our approach helped her realise early on that I saw her as important and would truly care for her, not just as extra "baggage" to be put up with because I was going out with her dad. We made, and make, time to spend together just us (as does her dad with her) and she turns to me with her joys and worries just as she does with her natural parents.
It's not how I would have planned to have a family - we still have the odd ex partner stresses and I sometimes feel sad that I missed out on the early years of motherhood - but I do feel that I am complete as a mother. I have a daughter who I love and who loves me. Our family might not look like other peoples but we know that for us it is perfect.