Talking this over with your boss is really important - and the sooner the better.
The second thing you should do is to keep to your hours, and take a proper lunchbreak. REPEAT AFTER ME: "I, Cazza, will work my contractual hours and will take a lunchbreak every day". There, that feels better

.
If you are working from 7.30 am to 9.00 pm then you are probably outside the EU working time directive, unless you have opted out of it, and
The third thing to do, is to prioritize your work: boss's work comes first.
And lastly ... you don't have to manage the unmanageable.
Best wishes,
Raindance