I just want to let you know that I adore my step mom, she is a great friend of mine and although as a step child sometimes it was difficult for me to feel like a part of the new family... she made me feel so included in her and my dad's childrens life, as well as our new family unit. I love her dearly <3.
Now, my step dad on the other hand was a monster, a total jerk and I dreaded even coming home from school because of him.
I really think that as hard as this situation is for you, a baby is much easier to adjust to, and befriend and love as the years go by

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I know my step mom was one of the best things that happened to me in my life!