Who taught you? Did you read a book? Which one?
I didn't think I would have any trouble with this being a step mom thing because I had a step son with my first marriage. But I adopted that child so... really, I was his only mom from the time he was 4.
The most difficult thing right now is dealing with my "bonus" son's mom. She complains to my husband about me A LOT! But it always seems like John and I are getting along well. I always heard that as a step.... you need to let the BP do the discipline and don't be thinking you are the same as the mom. So I pretty much am easy going with John. How to deal with the BM?