I highly recommend a Low GI (Low Glycaemic) diet, ideal for diabetics and people generally. Speak to your GP or ask to be referred to a Dietician.
Regarding the Alcohol, your Partner needs to stop. Not only will he worsen his Diabetes, if he's having up to 5 units per day, assuming he drinks 7 days per week then he'd be drinking up to 35 units per week, which is unsafe generally. Government recommendations suggest no more than 21 units per week for men. Your Partner is quite simply playing with his life.