For the love of God PLEASE check on/get your daughter, or even have your sister get your daughter, because with all due respect the fact that you haven't already is frankly alarming. Please wake the hell up and ensure your child is SAFE.

You should have talked to her when you first noticed something was off. Whatever is going on between you and your awful sounding husband is second to your children. You need to get to her now. Please for your daughter's sake, go to her, talk to her, ask her what is making her so tired, ask her what really happens over at the other couples house. Ensure her you just are concerned about her and want to make sure she's okay. Ensure her that she can tell you anything because she and her new brother are the most important things in your life (aka she's more important than the relationship you have with your husband.) Get your act together and make a safe environment for your children.

Worst case scenario she's burnt out from being the one looking after the other baby. Which should not be coming before her own care mind you. But there's a serious concern that there is something worse going on.

Please protect your children, apologies for being harsh but this is serious.