I've been there before. Not understanding why BM hates me so much, and why she would say horrible things to her kids about me. There have been plenty of nights behind closed doors the tears would just stream down my face for hours. But it will be harder for you seeing as how your emotions will already be all over the place because your prego. I can tell this. My boyfriend and I have talked about having kid together but we want to wait till my SKs are older, this is because we dont want them to feel like they are being replaced or that we will forget about them. I want as much time with my SKs as I can get before they become teenagers and no longer want to be around us..LOL...with girls its always the issue of Daddys little girl and her seeing you as someone who is taking daddy away from her. I would suggest you start a little game, First you have to find a way to play dress up or tea party or find out what she likes, this will be your bonding time, This will take you away from your husband but you need to build a relationship with her first. Do something special for both her and daddy while they are having time together but make sure its all about her. This will take the focus off of the fear your taking dads attention and make you apart of her life and gain her trust. I can explain more on PM. But if it worked for me whenn I was little then I no it will work for her.

Sorry you feel so bad I've also been there. Your BM is jealous and SD has regressed, because she's competing for dad's attention now with baby (aka your fault, even though its dad's too). Not that your baby is a fault! My BM and 2 skids (SS 10 and SS 12) are like 3 peas in a pod. DH and I are outsiders in their lives. She will not let us see them but 3 times a year then trash talks my DH on facebook how he is a "douche bag that should be sorry for hurting and confusing the boys by not knowing them". Well he'd know them if it wasn't for her manipulative ways. You can imagine the things she makes up about us to tell those boys.

Do your best to bond with your skids and involve them with the baby (this is how you feed/burp/change/whatever). Show them they aren't competing. If that doesn't work, you are in for a long haul. The good news is, it will end one day. The kids will grow up. We have 5 1/2 years of child support on one and 8 on the other, it used to be 15 and 17 years. Not that I want their childhoods to fly by, but our BM situation with the CS is terrible and not for this post. DH told me we could have another baby so soon I will be in your situation but with older children. You just have to keep on keeping on. It will be tough at times but DO NOT let that take away from your new baby. Only talk to your SD in a grown up voice though. I have a friend who talks baby to her 7 year old daughter and I wanna smack her for it! It makes them act immature. I never spoke to my son that way and he is very independent & mature. That should help her behavior over time. Try yoga, guided imagery, zoning out to music, getting lost in a hobby (sewing and baking are mine!), or anything to relax. Your bath is just time for you to cry. You need to be active but relaxed for your down time.

Take care of yourself and your baby. Feel free to PM me if you need another non-judgmental listener

Don't have any more kids. I know you're pregnant just don't do that again.

Stop identifying with his kids. You don't have 4 children counting the one in the oven. You have one plus one cooking. You'll never be mommy to 4 kids. Step parents don't exist. You're just the woman in Daddies life whom whey wish would go away.

Read the linked article carefully. Read it twice. It will save your marriage:

http://www.steptogether.org/disengaging.html

The 6yo will likely not remember becoming a big sister, but you can still capitalize on her being the big sister, and helping her teach her brother how to be a big brother. Help them learn how babies need to be taught a lot of things, and as the people closest to baby's age, they may remember some things better than you and Daddy do. That they can help you with the daily care when she's little, and as she gets older they can help her learn things. Involve them as you would any older sibling. (I found that my baby girl "bringing" her older brother a resent when she was born went a LONG way towards helping them bond. they are 19 & 21, and he STILL remembers the toy train, conductor's hat and whistle she "brought" him when she was born.)

Also, continue to encourage time with Dad on their own. Before and after baby comes.

Much of what you're seeing is pretty normal anxiety for kiddos expecting new siblings.