I know what you mean about your Sunday-night treat. I am the same way on Saturday night. I want a glass of wine at the end of the long week. I don't drink any other day, and I don't "cheat" with sugary foods or fried foods. I resent having to give up my only "vice" to stay on a diet, so I have had to find a way of working it in without feeling deprived and without double-crossing myself with "just one more glass." Here's what I have done:

I found a gourmet store that carries fine wine in little half bottles. I can finish the whole bottle because it only has a couple of glasses in it. I don't save money, because they're pretty snooty wines, but I also get to try some very expensive wines for no more than I would spend on a full bottle from the grocery store.

Or, I use recipes that call for wine. Pour yourselves a couple of glasses and use the rest in the food. Salmon is especially nice when poached in white wine. And a creamy sauce made with wine and butter is low carb, right?

It is important to find a way that you can live with in the long term, otherwise you'll go back to the "old ways" instead of staying with this forever.