New and need advice

Hi friends, I'm not sure where to start. I'm 185 pounds and dieting, losing anywhere from 1 to 2 pounds a week when I'm doing what I'm supposed to do and eating really clean. That's all fine and great but the problem is I'll have an event, a vacation, or a visitor come to town and then I have a few non-perfect meals and then the 8 pounds I lost over the last few weeks are back on in 1 weekend! I just keep losing and gaining the same weight and I know I am not going to be able to be perfect every day for the rest of my life. How do I get the weight to stay off even if I eat pizza and a dessert one night? when I was younger I could have eaten 75 pizzas and not put in any weight, these days I just have 1 unhealthy meal and gain 3 pounds. I physically don't even eat that much!

I'm a 50 year old female, 5 feet 4 inches tall, and weigh 185 pounds. I don't drink alcohol anymore and I've tried low carb, fasting, weight watchers, tracking calories, keto, etc. All the diets work but I continue to have the same problem. Now that the weather is warming up again I can get out and start walking more. That is all the exercise I'm currently doing. What else do I need to focus on in order drop the weight and have it stay dropped even after a "cheat" meal or vacation?

Any help or advice wood be appreciated. Thank you in advance!