I'll start by saying I was born and raised in a blended family so I personally know how difficult things can be or easy.

my SS is 7 and my SD is 4 and I'm now pregnant after having had a miscarriage in February that I had to go thru alone my SO plainly told me he didn't feel anything about it (his ex had a miscarriage he said he thinks the first it's traumatic after that these things happen which was devastating  for me) I'm now high risk pregnancy and my step kids don't know so I wear baggy clothes around them . my SO has made it so difficult for me in ways he doesn't understand like introducing me to his kids as his friend (instead of wife) so they are kids they ask why I sleep in the bed with him and where is my home etc his reason was he didn't want to upset his ex ,I honestly didn't expect to spend much time with them or him while he has them the weeekends, but after my miscarriage he completely flipped and told me I need to step up im their step mother. And I tried the best way I could (even tho they are still bratty because of him) he had no structure for them at all they slept when they wanted they drank juice all day no water he even often gave them sweets for dinner at their requests , so I gave them a bed time, I brush their teeth I potty trained my SD I cook for them etc and kids being kids they fought me on this and when I told him he said I just boss them around I don't show them affection, which I understand what he's saying but they never slept thru the night when we first moved in together and still proof is if I'm away they wake often in the night the stability I give them I see it's good for them they like it and are responding well to it,  now this is where his ex comes into play she tells them I'm not allowed to touch them or else their bad! Which as women we notice these small changes they sat next to me less they only asked their father for help with things stuff like  that. they tell me my mom said I can't hug you or else I'm a bad girl/boy even she had them yelling stranger danger when I would try to brush their hair before we go out to run errands, I tried to talk to my husband once about the first arised issue in the beginning which was my SS often looks at me for long periods (to the point my husband got uncomfortable and asked him why is he staring at me) or my SS will just burst in the room while I'm changing so I told him we need to teach him about knocking on the door when it's closed and my husband just said I was being tough on them because they aren't biologically mines my response was from a hurt place because At that point I already bonded with them (even tho he doesn't think so )if you don't trust them to be in my care let's make babysitting arrangements as he often works when they are at our house he got mad at me and said I was taking it personally , Even my sis in law and mother in law are witness to this and ask me why doesn't my husband do something, finally he witnessed the things their mom tells them to say or do and he got mad at the kids! I told him absolutely not they are children Ofcourse they are learning this from somewhere and I get it I try to explain to him I'm not here to step on anyones toes (he's afraid she will take the kids from him so whatever she says he won't disagree or stand up for his self or me!)

im now due in 3 weeks and I've begged him for counseling (he's said in the past how his ex was very emotionally/mentally abusive toward him that's why he snaps at me the way he does) I feel he often takes his anger out on me about that being a failed marriage, and I don't feel it's right that he tells me I'm a bad step parent but then continuesly ups and leaves them with me, I told him the first month after delivery I will be staying at my moms house and tbh I think I want a divorce he has a lot of unresolved issues with his ex , I don't think he's a bad parent I think he feels guilty for not staying with her for the sake of the kids (she often tells them to tell him I want you and mommy to get back together) 

When my father married my mom she had 3 kids already and completely stepped into the father role as their bio father wanted nothing to do with them when my mom had the rest of us she often felt guilty my older siblings didn't have their bio father like we did so she treated us differently she was more present and attentive towards them, I have a huge fear my husband is going down that road with my child. Me and my mom now have a great relationship because the last 3 years I've been working on it before then I had alot of resentment towards her and my older siblings , I'm scared that will be the case or that my husbands ex will tell my step kids to mistreat my child