I don't even know where to begin...coming to this chat room is not me at all, but it's worth trying. I am so stressed out with the whole stepmom thing, that lately I have started feeling like I regret my marriage. I feel like I just want to give up, cuz no matter what I do or how hard I try, it's never good enough for her or her mom. I get so overwhelmed and caught up that I get depressed and then my other children and my marriage suffer because of it.
I just lifted a prayer up for you CJH. I am a step father, so this comes from a place of understanding to a degree. I counted 10 instances of the word "I" in your original post. It's important to keep our focus on God and pleasing him. If you can focus your attention to what God wants, you can help find relief from your burden.
Matthew 11:30 For My yoke is easy and My burden is light.”
The above verse came to mind when I read you mentioning how overwhelmed and caught up you have been feeling. God wants us to focus on the good things in this life.
Philippians 4:8-9 Finally, brethren, whatever things are true, whatever things are noble, whatever things are just, whatever things are pure, whatever things are lovely, whatever things are of good report, if there is any virtue and if there is anything praiseworthy—meditate on these things. 9 The things which you learned and received and heard and saw in me, these do, and the God of peace will be with you.
The depression, the feeling of being overwhelmed is all coming from the source of where you are allowing your mind to focus. If you can shift it (even incremental changes help), you can find the peace of God that you seek.
In your post you mentioned that your marriage and other children suffering from all this burden you are having. As you make small changes and focus your sights back on the good in your life and the blessings you have, you'll also see an impact on your marriage and your other children.