You need to sit him down and tell him what you just told us. It does sound like she has some serious problems..

If he is unwilling to see a problem or seek help (in his parenting skills as well as his daughter's behavioral problems) then I would walk away. Love is not enough to make a relationship work. It takes work and your first priority needs to be your daughter. (it's a bit disturbing that she is 4 and lived with him a year and considers him 'daddy'. Where is her bio dad? Personally, I think it's a mistake to introduce kids, especially girls, to men and allow them to think of a BF as dad when there is clearly issues with his parenting and there is no long term commitment like marriage. Girls need a daddy but not just anyone will do. But that's just MY opinion)

From your post, you are no longer living with him, not married to him and he is doing nothing to fix the problem. Some of the symptoms you describe are indicative of a child that is being sexually abused. I'm no expert and I would not run to the authorities but if I were in your shoes, I'd be alarmed/concerned and look for other signs.

The primary problem is definitely with his parenting (or lack thereof). The child's behavior might be a result of his parenting and/or abuse/other disorder. Does mom have a BF/husband? Someone needs to look at why this child's behavior changed so drastically and progressively worse and it should be her parents. It's not your responsibility to fix this. If nobody does anything, then I probably would refer it to children's services so they can investigate and get the girl some help. When she is old enough to be in school, an official that sees that sort of behavior should also report it. (I was going to say they will but they don't always)

she has some impairments, maybe emotionally distrurbed, or maybe autism. dad has to address it is with pediatrician, it does not sound normal. it needs to be immidiatelly addressed with professionals, disciplining won't help.

These issues DO sound major!
And while Finedreams was pretty blunt, she may be onto something.
Are there any other indications that her development isn't normal?

How's her speech?
Conversation patterns?
Potty training?
Eating habits?
Does she know her colors?
Overly sensitive to textures, tastes, etc.?
Does she go to day care? And if so, how does she do?
Is it only you and your DD she's awful to?
Can she play with other children?
Does she play normally with her toys?

Any possibility she may have been abused? (Since you say her behavior has changed.)

Could you talk to the girl's mother at all?

I would be more concerned about why this child is acting out the way she is more than your SO's inability to discipline her. It sounds as if there is alot more going on with her than just a lack of discipline. Alot of what you describe can be associated with several disorders, including autism. However, the way you describe the change as being sudden and dramatic, it could be a sign of something even more disturbing. I would talk to SO about these possibilities and have him seek professional help for this child. Once you find out the underlying cause, you can determine a behavior plan appropriate for the situation.

If you love him, I would give him a chance to get to the root of the issue. If he is not willing to do anything to better the situation, then I would walk away. No matter how much you love him, it will not change the problems with his child.

children with ASD sometimes regress rather dramatically all of a sudden. doesn't have to be abuse necessarilly. but doctor's appt needs to be made immidiatelly. I agree with ima that your little girl considering your BF to be her daddy is a bit off. is she going to call every BF of yours 'daddy"? If i would be you I would tell BF what i think about doctor's appt needed to be done immidiatelly and if he does not follow through I would leave a realtionship and call the authorities. Not taking children to pediatricians when it is necessary is a form of neglect.

I don't know what to make of the whole situation. My child has autism and some might have described him as "violent" at that age, but he had other developmental issues...like delayed speech, fixation of patterns, arranging toys in a line. obsessive tendencies. However, he is no longer "violent" because I was able to give him replacement behaviors for when he's frustrated.

So, it would come down to parenting either way. If there is a developmental issue or mental health issue, those need to be addressed. She might be an abuse victim as another poster pointed out. Whatever it is, it doesn't sound like your SO is willing to work through the problem. I don't think I would stay in that relationship.

That's why I was asking about other developmental areas -- to see if it sounded like autism or related...

OP - If you have any input, try to get her seen by someone who is familiar with autism spectrum disorders and with abuse in young children. Too often, 'regular' pediatricians rush to reassure the parents when there really IS something wrong with the child. (My son's pediatrician 'shined me on' for more than 18 months with platitudes after I was sure there was something wrong. His autism wasn't diagnosed until age 4 and I had been bringing up valid concerns since 6 weeks!)

I just wanted to clarify what I meant, because I don't know if others interpreted my post as saying dad needs to 'discipline' because that was not what I said. (If that came from another poster, I apologize but I didn't see any post that said 'discipline' in it)

I said that I believe "The primary problem is definitely with his parenting (or lack thereof)." That means that dad needs to parent, not necessarily discipline. (discipline is only a part of parenting) Another part of parenting is, in my opinion, recognizing our child's needs and if there are behavioral problems, there are causes other than lack of discipline. As FD said, it could be a medical problem or developmental issue... but if dad is unwilling to see or acknowledge the problem, then he is lacking in his parenting. It's his responsibility to recognize problems with his child and get the child proper care and/or treatment.

I have a student whose mother was brought him to every possible doctor, educator, psychologist since he was like 12 months old trying to find out what is wrong with him (would not do what he is told unless you repeat 5 times, normal IQ and no hearing impairment), they ignored her pretty much saying there is nothing wrong wiht him, you are young inexperienced mother. She was at the end of her rope when he was finally diagnozed at 13-14 with pretty severe auditory processing disorder. It is not only speech for him, he would take long time finding out if the specific sound is train passing by, airplane flying or birds chirping or school bell. I mean severe problem. Of course he would not do what he is told because he does not process. But mom never gave up and finally got the answer. If this dad is unwilling to look for the answers, it is only going to get worse.