Well, I've joined groups on Facebook, now I'm going to try this out.  
 

im completely lost and pulled between love for my fiancé and my sanity with my future step daughter. 
 

a little back story, I am 32 years old. I have two biological children and currently one future step daughter. I was married 5 years ago to another man who had 2 children from a previous relationship, so this isn’t my first time being a “bonus mom”. But this time, I am really struggling with her temper and all around attitude. She is only 3 and I have been in the picture since she was 9 months old. 
 

so that I don't have a million hims and hers, I'll call them by their middle names. Amielia is the 3 year old, Marie is the bio mom and Levi is my fiancé. 
 

marie sleeps with Amelia in her bed. She is single, with no man living with her so some may find it appropriate. But when Amelia is here, we do not allow her to sleep in our bed with us. Both of us are comfortable sleeping nude and it's not appropriate to have a 3 year old cuddling with her daddy or future step mom when they are nude or even in boxers. She is a very touchy girl so she will lay in bed with you and rub your face, your neck and it's just not something that I or Levi are comfortable with. So when we make her go to her own bed, total hell arises. She will scream and throw things; she has even went as far as getting out of her bed and hitting her head off of her door. We have a video monitor in her room and I'll let her scream until she starts hurting herself, that's when one of us steps in and places her back into her bed. 
So bedtime is never a pleasant time.  I've tried letting her fall asleep with me then placing her in her bed. But when she wakes up and reaches to touch someone, out comes the temper. I typically have to go and sit in her bedroom floor and just put my hand on her back and she goes back to sleep. A child the age of 3 should not be this clingy and needy that she has to have someone continuously touching her just to sleep. Right??

her mom still let's her have a Binkie. Her teeth are already messed up where she has it in her mouth constantly. Every picture she sends us while she has Amelia, the Binkie is in her mouth. 
we don't give jt to her. When Marie and Levi meet to exchange Amelia, Amelia knows.  She gets in our truck, takes it out and hands it to either me or Levi. And when she gets into her moms car, she starts pointing to her mouth and grunting and Marie instantly gives it to her. 
I believe this is the reason Amelia isn't talking.  She had a vocabulary of no more then 25 words that you can understand. The rest of the time she just points and says hey. I try to make her say whatever she wants. Milk. Juice. Baby. Dog. But when I say, "you have to tell me what you want, say the word _____". She goes into a fit. 
she smacks me, tells me no when I ask her to do something. When I ask again she screams No!!!! At me and then will run away and scream and cry sitting in a room away from people.  
she isn't potty trained and she will not allow you to help her use the potty.  She hides and when you say are you pooping, she holds her hand up and screams no no no no and if you put her on the potty, she won't go.  She has made herself be almost impacted because she refuses to use the potty. If you walk into a room while she's in there and pooping she will point at you and scream the word " OUT!!" And point at the door. 
We have tried time outs, taking things away, about every form of punishment you can think of for the behaviors. I'm at a loss. I don't know what else to do. 
her behavior has put a strain on mine and Levi's relationship. I used to love spending time together, I even quit my job so I could be home and help Levi out because he is a new dad and he just thought he was doing something wrong. But now I see, he wasn't.

levi works at a job where he is gone for 4 weeks at a time, and during that 4 weeks she is with Marie non stop. When he is home we have her 5 days out of the week. It used to be the first week would be hell then the following 3 would be amazing. But the last 3 months, the happy times are few and far between. 
 

ive considered her behavior problems may be something psychological. But she doesn't show any signs of being on the autistic spectrum. Marie brought up the behaviors and Marie said the doctor said Amelia is having separation anxiety because she misses her real mommy and daddy being together. But she was 3 months old when they split up so there's no way she even remembers a day when they were living together. I believed Marie made up that diagnosis just to hurt Levi. Levi asked the doctor himself about the diagnosis and he said he's never said that. 
 

so any advice would be greatly appreciated. I'm on the verge of leaving because I love spending time with Levi, I love when he comes home from work, but I'm dreading the day we go pick up Amelia. And I feel so guilty for feeling this way but it is so hard dealing with this.  I have never seen a child behave the way she does.  
please, for the sake of my happiness and my relationship, tell me what to do.