Stepmother demands that 16-year-old stepson stay to care for her children even after she and his father are separated: 'She tried to say she had raised me for 9 years and should be allowed to keep me in her and my half-siblings' lives even if dad isn't'

Relationships, even our closest relationships, are complicated. As we change and drift through our lives, we'll find that the foundations on which they are built change and become no longer relevant. 

If someone had a significant impact on your life and remains significant and supportive in your life, there's a good chance that that relationship will persist through many changes. But if the emotional connection isn't there, you can't grasp harder and force it to remain intact. That will just cause it to break more rapidly, all the same.

There are a myriad of factors here that distance the teen from his father and stepmother's household, and from the obligation of being a part of their life altogether.

For one thing, custody has shifted fully to his mother; he no longer has any legal court-ordered guardianship of his father's and stepmother's household. For another, his father is separated from the stepmother and isn't even present in the household at all. So, really, it isn't his father and stepmother's household; it is just her household.

Sure, he might want to maintain some contact with his half-siblings, but those relationships can be challenging and, well, unfortunately, relationships with siblings, even full siblings, tend to be determined by how and where you end up as adults. Again, the relationship will be determined by the impact and connection rather than just the convenience of a simple relationship.