How do I stay connected to my stepchild if their other parent is hostile to me?

This is one of the hardest positions—you're caught between loving someone and being actively resented by someone else who has legal power. First, protect your partnership. A hostile co-parent will try to drive wedges, and if you and your partner aren't solid, you're already lost. Second, never speak badly about the other parent to your stepchild, even when provoked. Your stepchild needs permission to love both parents without shame. Third, show up consistently anyway. Not to prove anything, but because your stepchild shouldn't have to choose or lose relationships because adults are in conflict. They'll notice who remained steady. Some co-parents eventually soften when they see you're genuinely invested in the child's wellbeing, not the relationship with them. Others never do. You can't control that. What you can control is your own integrity—staying kind, keeping boundaries firm, and never using your stepchild as a messenger or bargaining chip. The gift you give them is stability and belonging in a fractured situation. That matters more than the other parent's approval.