Don't jump to conclusions. Just sitting in cooler damp temperatures condensation occurs and put water in the oil. It doesn't take much water in the oil to make it milky. Before jumping in and tearing it apart I would sure change the oil and filter and drive it and do some more checking. Yes head gaskets do at time go out but not near as frequently as I see it brought up here. If there are no other signs of performance loss or coolant loss you don't have a head gasket out. It will be brought up to run it with the radiator cap off and look for bubbles. Well you had better know how to distinguish between normal turbulance bubbles and compression leak bubbles. For now change the oil and filter and drive it and see what happens.