Not good enough again

I hate feeling like I need to prove to my children that I am good enough for them. I hate when they make me feel that I'm not, when I know that somewhere in their head they are wishing they were still with their birth mother. I hate the fear that someday they will leave, that despite all I do they will choose to go to her and leave behind our family. How do I make all these feelings go away??? I have 2 children that are very good at bringing those feelings out in me. Making me feel that I'm just not good enough, that I'll never make it raising them, and that they really don't want to be here. I know that they have those days, I know that that is part of our life, but it doesn't make the hurt go away. When I look into their eyes and see confusion, and anger I just want to cry. Why can someone do the terrible things that she did to them, but yet they don't see that. I know there are reasons, I know that children always see their mother as wonderful no matter what she does or did, I know that, but don't always feel it in my heart. At times when I try to reach out to them and they pull away I don't think they know how very much it hurts. I know that as one of my children sees the things his "friends" from school are able to do, they can watch movies we don't watch, run around town whenever they want, they have name brand whatever they want, have game boys and x-box and all the things we don't have, I know that makes him jealous, and I know that in his head he would have those things if he wasn't a part of our family. But yet, this is the way our family is, and I wouldn't change our standards, or our lifestyle for any of my children. I just wish that it didn't hurt so bad.