Welcome! and good luck on your W/L Journey
I have a fiance who is very much like your b/f, who has this amazing metabolism!
He is also wanting to 'bulk' up and was told to eat more!
which means we have more food around the house and he is eating more meals in-fornt of me
It makes temptation for me difficult! But i try to tell myself i am a stronger person if i can stop myself indulging, sometimes this works, sometimes it doesn't.
With struggling on the weekend, perhaps try to identify what causes you to struggle and then see how you can change that trigger, it may be boredom, time management, temptation or similar. Once you identify it may be easier to manage, also try to convince yourself failing your diet on w/e's un-does all your weeks hard work