My girlfriend (now fiance) of 8 years have been together for as long as my 8 year old son can remember. We are in our late 20s. We have lived together for 6 years and he has lived with us for about 5 years. We also have a 6 year old daughter together. His mother and her situation is a whole other animal (she was young when she had him, he has an older and younger brother over there, she lives with her "husband" at her parents house and is due with another child in a couple days) and not the source of my growing frustration; it is what it is there. I do not know who, if either of us, is in the wrong but I can't help feeling like it's not me (fully understanding I am not perfect). So my issue is that my fiance treats my children differently and completely refuses to acknowledge that after 8 years (5 of which my son has lived with us full time) she is his full-time mother figure. My son has been acting out a lot lately due to this situation and the one he is in with his actual mother. She wants what is best for both of my kids, but holds my daughter on a pedestal and treats my son like he is just screwing up "her daughter". I think my son needs a more involved mother figure because he certainly doesn't get it with his actual mother. Most of the time I feel like she resents the situation we are put in with his mother and takes it out on my son. Constantly when we argue about it she tries to explain that he is not her child and my daughter is, so therefore not in anyway her responsibility. I try to explain that after this long, I believe she should accept that she has a motherly responsibility to him and that any normal person in our situation would treat him like their own son. Am I wrong? I love my kids and I love my fiance and am afraid that this is going to tear our family apart. Thank you to anyone who might try to help and took the time to read this.