Fast food makes an INSANE profit on fountain drinks. If you’re hooked on soda like that- I’d say go to the nearest grocery store to get a 2 liter one for the same price instead. I empathize with wanting to give yourself some kind of a treat. I am amid similar struggles, but staying frugal while achieving the reward can remove some guilt which keeps it enjoyable. I wish you the best. I’m so sorry that your wife is not well and I hope she feels stronger very soon.