You definitely have a faulty thermostat that opens much earlier than it should. With the AC off, you should notice the same at highway speeds. The temperature, with a good thermostat, a good radiator, a good fan and a good coolant temperature sensor, should, after the engine had enough time to warm up, stay steady at the thermostat's opening temperature or slightly below it, but still steady, no matter what the vehicle's speed.
To test if the thermostat is faulty: look at the cooling system plumbing of your car and touch a pipe that looks like it directly links the thermostat housing with the radiator. Look for your engine's data and identify at which temperature the thermostat is designed to open flow to the radiator. Provided that you have a temperature gauge in your instruments cluster, if that pipe becomes warm/hot when the temperature is lower than the thermostat opening threshold, your thermostat is opening at a too low coolant temperature and it needs to be changed.
If the condenser uses the same radiator fan to cool down, the system is wired so that, whenever the AC system is on, the radiator fan switches on whenever an intermediate pressure is detected by a pressure switch or sensor on the refrigerant liquid line, so that the compressor's discharge pressure can be lowered. If coolant is flowing through the radiator at the same time, that coolant gets cooled too, even if the car is stationary.
Along with the thermostat, i recommend you to also replace the coolant temperature sensor. They're cheap and easy to change, and tend to become inaccurate when old. In addition, in modern cars, the ECU uses the coolant temperature value to adjust the fuel air mixture and other important engine running parameters, so it's an important part.