Create a variable and set value false.
private bool button1Clicked = false;
On button1 Click event set value to true.
private void button1_Click(object sender, EventArgs e)
{
button1Clicked = true;
}
Now If
button1Clicked
is true means button1 clicked else no.
private void button2_Click(object sender, EventArgs e)
{
if (button1Clicked)
{
}
else
{
}
}