Well, I don't want to hurt your feelings... but yes, your dog is fat. I won't be gentle and say cuddly

Or use any other words that don't reflect the reality (so you can't be tempted to ignore it, or be lulled into some sense that it's not a serious situation). He is more than a little overweight, and you really
need to do something about it. Rather like with humans, a great many health conditions are caused by excess fat - and some are life-threateningly serious.
Some other observations: You should NOT be feeding an overweight dog the amount recommended for a dog of that weight. If you do, he'll just get fatter. Feeding guidelines don't refer to actual weight, they refer to IDEAL weight. I don't know how tall your dog is (how tall
is he?), but the ideal weight for most male boxers is in the region of 65-75lb....
Sooo - having cleared out of the way the question of "is he, or isn't he" (he IS), how about some suggestions for what to do about it?
1. As ever, the first step to losing weight - whether you're human or canine - is *exercise*. There aren't too many of us that can effectively lose weight on diet alone. So, you need to sensibly increase his exercise levels. As a guide, a boxer should have at least an hour, preferably two or more, of good hard *running* exercise daily (leash walks don't count). If he's a long way off that currently, then you'd need to work up to it. But long term, that is what he requires.
2. Feed a better food, and one that isn't loaded with junk carbohydrates (as what you're currently feeding is). Dogs can't digest carbs well (not evolved for it) so they tend to be broken down to complex sugars and stored as fat. Don't bother with so-called diet foods - they rarely work, because most are loaded with carbs and cut the good nutrition (protein and fat) instead. And that just compounds the problem. You might consider trying a high protein/med-high fat/LOW CARB food instead - something like Innova EVO, Orijen or NV Instinct.
3. Don't feed a dog that should weigh 75lb an amount appropriate for a dog who should weigh 100lb. Feed him for 75lb, or slightly *less*.
4. If the dog gets too hungry, add some cooked green beans to his diet. He won't get much out of those nutritionally (which is the point) but they will fill him up. If he's hungry enough, he'll eat them (and if he's not, don't worry about him).
5. *Watch the treats*. If you must give treats, reduce the amount of food at dinner time. It's incredible how many calories some dog treats contain (as well as other undesirables...