I think it is probably only human to be nostalgic for past "special" relationships. The key to it is whether your BF is aware of it or not... if not, there is no problem... if he is aware that something is awry, you have kind of answered your own question yolande.... you have said yourself that you wouldn't like it if your BF hankered after the past in the same way.
I think we are genetically programmed to enjoy wallowing in nostalgic bittersweet memories from time to time.... just remember that life moves on, and most importantly of all, we all change over time... the past is another country, and the person you remember is not necessarily there anymore.