Forchantly he is 2 and not older, he won't retain the memories as long and will tend to new things around him. If it has been since Christmas he should be asking about his father less and less. When he gets older he may ask more detail questions and you can should answer them as they happen. Just always keep in mind his age and what he can understand. An easy way of doing this is by looking at another child the same age as your son that you may know and determining what he would understand.
Parents tend to give more credit to thier own child in regards of what they can do and understand.
But just don't lie to him and let him know how much you love him.