Didn't understand exactly how your two LBs are linked...
But you can get the index of first selected item and use it to get second item:
for (int i = 0; i < ListBox1.Items.Count; i++)
{
if (ListBox1.Items[i].Selected)
{
lbltrainer.Text = ListBox2.Items[i].Value;
}
}
Let me know if I misunderstood.