Losing and regaining the same weight

How much weight are we talking about? If it's relatively a lot, like 10%+ of a sensible goal weight for you, that's good advice above (and I'll add some comments later in this post). If it's 5 pounds or thereabouts up and down, I'd personally call that maintenance - maintenance is realistically a range of a few pounds for most of us, not one specific exact weight.

If you're repeatedly gaining more than that few pounds, that's something to work on specifically: Keeping within a few pounds.

Decide on an upper limit, either on the scale, or the fit of some specific clothing item(s), tape measurements, or whatever. Then monitor regularly. If you hit the limit, or start creeping close to it, cut back a bit on the eating side, or add a little activity, until your weight creeps back down to the bottom of the range. Don't let it get out of hand.

If it's more, I agree with Sinisterbarbie1's advice.

Too many people treat weight loss as a project with an end date using extreme measures, as if being overweight were a sin we needed to suffer in order to expiate. Typically, that involves restrictive eating rules (details vary), and/or intense exercise. After goal is reached, the person immediately or gradually "goes back to normal", and regains weight.

In reality, weight management is a lifelong endeavor, at least for those of us with a tendency toward overweight.

IMO, that puts a premium on experimenting and finding - sometime during weight loss - reasonably enjoyable (or at least tolerable) eating and activity habits, then practicing those habits until they can continue nearly on autopilot when other parts of life get complicated . . . because that will happen.

Exactly how that looks will vary by individual, because personalization is key. Some generalities:

1. On the eating front, figure out eating patterns (food choices and timing) that balance appropriate calories, reasonable overall nutrition, good satiation, happiness (tastiness), practicality, and affordability.

If you're not going to permanently forswear parties, restaurants, dinners at friends' homes, potlucks, happy hours, holidays, celebrations, then figure out how to make those work, sometime during weight loss. (I'd note that a rare over-calorie day isn't doom: It's a small drop in a big ocean. The majority of our days determine the majority of our outcomes.)

If, to be happy, you want a glass of wine on Friday/Saturday night, or a fast food meal or two each week, or a bit of something chocolate in the evening, figure out how to fit that in. Some people can moderate some foods, not others. If you can moderate a food, have a small portion that fits in, more often. If you can't moderate it, but must eat some sometimes to be happy, figure out how to either acquire only a limited portion (eat cake only at a restaurant, one ice cream cone from an ice cream parlor instead of buying the quart/liter of it, bank some calories for an indulgence once a month, whatever).

If you don't like green smoothies, kale, or some other so-called "superfood", don't eat it. They're not magic.

The goal is to get decent overall nutrition at reasonable calories over a day or few, via the totality of one's eating. It isn't to never eat an "unhealthy" food ever again (other than things that are literally poisonous or that you're allergic to).

Thinking of individual foods as "good/healthy" and "bad/unhealthy" isn't helpful in this context, IMO. It's important to get good overall nutrition, but that's about how various foods are combined over time. In practice, I find that if I focus on getting the good stuff (filling, nutritious, tasty) into my overall eating patterns at reasonable calories, the less nutrient-dense foods reduce almost automatically.

Food isn't sin, guilt or drama around it just aren't helpful, IMO.

2. On the activity side of the equation, find ways to move more that fit into your life with good life balance, i.e., enough time and energy left for everything else important to you, such as family, job, social life, non-exercise hobbies, etc. "Activity" is a combination of daily life movement, and intentional exercise.

Sometimes, people think only extreme, intense exercise is beneficial. That's 100% a myth, whether the goal is fitness improvement or increased calorie burn. Find something you enjoy doing, or at least tolerate well, that fits into your schedule. An exercise we enjoy and want to do regularly is 100% more beneficial than something that makes us miserable so that we procrastinate and avoid it at the slightest excuse.

Whatever exercise that is, do it at a frequency/duration/intensity that it's just a small, manageable bit of a challenge. That small challenge is what creates fitness progress. As you get fitter, and it gets easy, increase the duration, frequency, intensity or activity type to keep that manageable challenge in the picture. Exercising to exhaustion is counter-productive: It makes us rest more, which reduces calorie burn from daily life.

On that daily life activity front, there are lots of ways to create more movement in your day, without devoting a bunch of additional time. It's about creating habits of movement, in place of habits of inactivity. There's a whole thread here, with various people's strategies/ideas:

http://community.myfitnesspal.com/en/discussion/10610953/neat-improvement-strategies-to-improve-weight-loss/p1

You can do this. It's not about "motivation" and "willpower", if you ask me. It's about experimenting, finding and establishing congenial new habits that can become a new and improved autopilot daily routine, and putting in place some kind of limit-monitoring practice so that corrections happen before regain gets out of hand (if it happens).

Morning. This is something I posted on someone else’s thread yesterday. She and I were both looking for motivation.
“I too have fallen off the wagon in recent days and am reaching out for motivation this morning, so was pleased to see your post. For me the trick is remembering it is not about depriving myself until I reach a goal weight and then reverting to bad habits. It’s about healthy and happy lifelong change. Great food, smaller portions, more movement. What has helped me is delicious salad chopped two days in advance and kept covered in the fridge. Multicoloured veg, with some nuts and dried fruit. Two cups at lunch, two cups at dinner with any kind of protein. Delicious and satisfying. It forms the heart of the meal. Hope that helps. I have lost 16kg since Jan 4. Five to go.”
And about desperate goals: “ If I think about how long it takes me to gain weight, it’s not in a rush, but a steady incremental unacknowledged turn in one direction. So losing it is about facing another direction, but being kind to yourself as you do. For me it was unconscious eating: too much of everything. Now I pay better attention, but go gently and enjoy it. And yes, being organised takes the stress out.”