In order to maintain your healthy weight for life, you need to learn new behavioural habits to replace the ones that contributed to your weight gain. We call them the habits of healthy weight people. Once you have mastered them you really will be able to relax at your ideal weight.
Most people believe their ideal weight is a definite number. When you are trying to lose weight and set a target that seems perfectly reasonable, but this is virtually impossible. It's like expecting your car to always weigh the same no matter how many people are in it. Try not to place too much importance on a particular number - the most important thing is to feel happy in yourself and feel good about how you look.
Having lost your excess weight, you believe you're in the right mind set to keep it off. You feel empowered like there's nothing you can't do. After all, this is one of the most significant achievements of your life. Unfortunately, your mind isn't wired that way. Evolution has taught your body that having extra body fat to spare is better for survival than having none at all. So your instincts are only doing its job when it distracts you from noticing future weight gain.