Why is staying single cheaper? My girlfriend and I save a lot of money by being able to share an apartment and splitting the rent, internet connection etc. Living alone would be much more expensive for each of us.

sharing a place tends to be a lot cheaper - but note that many people who are single do not live alone.

congratulations to the only comment in the whole comments section that mentions kids or children.

like always, there's an XKCD for that: http://xkcd.com/946/

..and like someone mentioned their 200$ food budget, try spending twice that amount on kindergarden a month that your kid is not attending for now because he's home sick and you're spending extra on treatment.

When you've exhausted your saving options, making more is still the best option for saving money:) Simple math, if you spend 3000/month of your favourite currency, then you'll have twice more money by earning 4000 vs 3500.

More realistic advice: live like you would at 2/3 your income and use the extra 1/3 to optimize for low cost as necessary.

Stay single, save money, die and leave your paper trinkets for someone who will actually spend it to raise another human being