DH and I had been living together for about 2 years, joint finances, both of our names on the house/cars, etc. At the time we had no desire to make it official and get married. We felt that the cost of the wedding we were expected to have could be better used elsewhere and were secure in our relationship married or not.
DH has 50/50 custody, so SD, who was 6 at the time, spent a lot of her time with us. I was acting in a full on SM role, at BM and DH's request, caring for SD when both parents were otherwise engaged, on top of the 50/50 split, (DH working, BM auditioning husbands). SD really disliked introducing me as "my dad's girfriend" and begged us to let her call me her step-mom. She said that she wanted to tell people I was something to HER, not just to her dad. We could understand that line of reasoning so we agreed.
BM heard about this and told SD that she was not allowed to call me her SM, and that I was "just" her dad's girlfriend. Of course this upset SD and opened a whole other can of worms with SD questioning why her mom "obviously" didn't like me.
On the surface I can understand that I was not SD's SM, as we were not married. But at the time SD called BM's roommate's daughter her sister, called various unrelated adults aunt and uncle.
So, am I right to feel offended or am I being overly sensitive?