One day I was driving it the next day he would turn over but not start

If he did something to it, he probably would have put a bad relay in under the hood. Or unplugged your coil wire. Either way it sounds like you have either no fuel or no spark. You can just pull a plug wire and check for spark easily enough. It is a 1990, so it wouldn't be out to the question to have a bad fuel pump. See if you can hear the fuel pump hum. Touch a large screw driver to the bottom of the fuel tank, put your ear to the plastic handle. Have someone turn the key to Accessory. You should hear the pump kick on. If no noise, check you fuel pump relay. If relay is good, you most likely have a bad pump. He could have sold you the truck knowing the pump was bad. Sometimes if you bang on the bottom of the tank, it will come back to life for a little while.

Check for fuel and soark first