It is not uncommon when starting out in Wicca to use general terms for the God and Goddess, such as Lord and Lady, or Mother Earth and Father Sky. Then as you progress you come to realize that the deities are making themselves known to you by different names. And that's perfectly normal and perfectly alright.
There is also the concept within Wicca of Patron deities, the particular God and Goddess with whom you have a special relationship. This doesn't deny the existence of other deities. Rather it is as if they are your close friends and the others are simply acquaintences.
Sometimes Patron deities stick with us for a lifetime. Sometimes they only come to teach us particular lessons we need to learn. The ones who come to teach us are called Tutelary Deities. They teach, and when we have learned their lesson they move on so that another might take their place.
I think the idea of thanking your Mother Earth and Father Sky and giving them both an explanation and an offering is a good one. I don't believe you are betraying them. You simply have moved on to the next step in your practices and beliefs.