The bus driver looks back and sees/to see two men fight at the back of the bus. The bus driver pulls to a stop and goes to pull them apart. As the men have calmed, the bus driver goes back behind the wheel and drives on. But seconds later he hears something. He looks back and sees/to see the two men are fighting again.
When is it okay to use to see?
There is very little difference between the two usages. "Looks back to see" may possibly have connotations that he looks back in order to see what's going on: that is, he can hear a kerfuffle, and so turns his head so as to look at what's going on.
"Looks back and sees" is more that he happens to turn his head around towards the back, and because of that he notices what's going on. There is no intention to investigate.
