Leave No Trace Ending Explained (Spoilers)
While it wasn’t made 100% clear when Will decided to raise Tom out in the woods, what does become clear is Tom comes to like the idea of living indoors. After meeting a nice boy at a farm, it becomes clear to her she wants to be around other kids, guys specifically, and get to know people truly. That is, beyond coming with her dad to the VA hospital to get pills to sell. Hence when she comes across a place which offers a community, stability, for the second time in a few weeks, she decides she can’t run away with her dad again to who knows where.
Don’t get me wrong, she still loves her father deeply. It is just, she can’t run away from problems she doesn’t have. His inability to function in society is his issue, not hers. And while it will surely be hard with her mother dead and dad who knows where, with no real means to track him, she can’t keep going on like this. According to that social worker, her academic performance is beyond her age, so all she needs now is a place to stay, a school to go to, and she can maybe have normalcy – stability.
Something that, even though Will loves Tom, he gets. So rather than pull the “I’m your father” card, or anything like that, he simply understands and lets her go. He lets someone probably not even 16 live her own life and focuses on his. One which will be somewhere out in the woods.