Your portion sizes are not fine - otherwise you wouldn't have put the weight on. Weight loss is all a matter of calories in and calories out. So if every day you eat just 50 calories more than you need (half a banana or a very small apple), then in five years' time, you will be about 26 pounds heavier.
It often happens in couples that both people get the same portion irrespective of their actual needs. However, a man with my stats (height, weight, age and activity levels) can eat 200 calories a day more than me and maintain his weight. If I eat at his level - I will be 20lbs heavier this time next year. A woman who is just 2 inches taller and slightly more active, can eat over 320 calories more than me (if I eat along, I will end up 33lbs heavier in a year). It's really easy to eat more than you need.
For lifestyle changes to stick, they need to be small, sustainable and welcome. For instance, I cannot imagine limiting my carbs so LCHF is not for me (not to mention it's not healthy in the long term). Through trial and error, I worked out that for me to feel satisfied with my meal, it has to be high volume. So I cut out alcohol, added sugar and fat, meat and processed foods (including juices); severely limited dairy and eggs and included more servings of non-starchy veg, wholegrains and legumes. I also use a lot more spices and herbs to flavour my meals (and for their health benefits). This way I'm getting visually bigger portions that taste amazing but they have fewer calories. I still have things like pizza, crisps or ice cream but very rarely and, when I do, I have lower calorie meals for the rest of the day (eg a huge bowl of salad with beans and courgetti with tomato sauce).
It took me about three years to make all those changes and I didn't rush it. I started with calorie counting (I use the free web version of Cronometer) to see where I was. It was a pain to weigh everything out in grams and log it but, after a while, it became second nature. Then I looked at easy wins. I started drinking fewer coffees. I started adding less sugar - I went from 2 tsp to zero in half teaspoon increments over several months. Now I can't imagine adding sugar. The small changes really add up and your taste buds adjust over time.