Cutting and Maintaing at the Same Time

sorry if these are newbie questions,

ive had a few months off due to personal reasons, diet went to crap, but now im back into it,

so if I am trying to lose the belly fat while training my butt off,

am I trying to get as close as possible to calories in vs out?

I understand that to lose the fat, you have to have a higher calorie deficiency,

but wont I start losing muscle if im calorie deficient?

at present my training is like this

4 day split, train 6 times per week, after each session, a 25min cardio session on the treadmill, fast walking pace

Currently, eating 3 meals per day + 2 shakes, meal 1 eggs + veg, meal 2+3 meat and veg,
ill snack on some nuts and/or muesli with skim milk if im hungry

ive been back on my training for 4 weeks now and havent touched any white bread, rice, pasta, noodles

am I on the right track?

edit: if one of my meals on the weekend had to be a calorie fest, does it matter if its eat anything you want or eat as much as you want but clean? eg buffet, where you just eat veg, seafood, meat, no desserts, no dirty carbs
just trying to get my head around it

thanks eveyrone