Not able to stay consistent

I have been trying to lose weight for over a year now.My bmi is in the normal range so I am not unhealthy however I am noticing a double chin, flabby arms ect. I start strong I maybe even lose some water weight and then I go downhill Then a month later i start again and it's a never ending loop

How do i actually stay consistent on my diet - I play football 4-5 times a week so activity isn't a problem but it's my diet that gets affected

How do i stay consistent enough to lose ten kg