I am also trying to budget in order to free up cash - in my case for debt repayment.
For me, a spending diary is a bit of a pain. My solution is to withdraw €200 per week, on the same day each week. I use this money for; buying food, socialising (don't drink or smoke), buying petrol, getting new clothes, haircuts etc. Basically, it covers everything except household bills and big ticket items like car tax and insurance.
It often means that I'm a bit short near the end of the week, and sometimes I have to dip into my savings, but overall it's working for me.
Just thought I'd post it as an altenative idea to a spending diary. The ideas above re cutting back are good. Have you thought about living together in a one bed apt. That, depending on your location, could cut your monthly spend on rent and utilities.
Finally have a look at what you are saving for, a wedding, new house etc are all pretty expensive. Doing them all in such a short space of time, especially when you have large debt to service, is a real challange.
Best of luck with whatever you decide, and well done for facing up to this.