Wow - sorry for the delay on responding to your kind replies. I didn't notice that there had been activity on this thread until now - my apologies.
Happyflowergirl - thanks - I agree - my dad should not have put this responsibility on me, but too late now.
I have talked to my stepmom about how I feel, and she acknowledged that it's easier to feel closer to her biological kids than to a stepchild. Mind you, I didn't even know her until I was 18, so it's not like I grew up with her. I don't blame her - as I said, intellectually, I "get" it. If I still had a mom, I doubt that I would have this strong need for a mother figure in my life.
Wow - I'm just realizing how powerful my feelings are about this - not about my stepmom in particular, but how I probably really never got over my mom's death. I kind of thought I had, but maybe this situation with my stepmom might be bothering me more than I realized, for reasons I never stopped to think about...
Anyway, you raised a good point about my other stepbrother - I don't know if he feels neglected or affected by my stepmom's preference to live near her other son. I don't think he does, but then again, he still has his dad, and two other women that he has a "stepmom" relationship with (his dad recently divorced and remarried a woman that he had dated in high school". He has never lost a parent, so that's reminding me that it might be bothering me significantly more because I have no biological parents left.
AAAAA - that's interesting about things being easier to explain to your daughter when she was a child as opposed to as a teen/adult. I would have thought the opposite, but your words are reassuring.
Thanks again everyone - you've given me a lot to think about...