Living together is not the same as being married, you avoid the possibility of divorce but your financial rights within the relationship are very different.
There's no such thing as a Common Law Marriage
Couples living together often believe that they are each regarded as a ‘common law spouse' and therefore legally protected in the same way as married couples. This is not true. There is no such a concept as 'common law marriage' and you're not legally viewed as a 'common law spouse'. Cohabiting couples may well be put at a financial disadvantage both in the present and also in the future should one of you die or the relationship breaks down.
Get a will - it's the only way
It is a really good idea for both of you to have a will otherwise you will die ‘intestate'. Apart from sounding both unpleasant and possibly painful it means that your home, finances and everything you owned right down to the Victorian long case clock or the Zepplin vinyl will be parceled out according to Law of Intestacy, which could well be against your personal wishes. In many circumstances this means that your partner's property would be left to their next of kin, their parents or children and not you. This distribution of assets will be very different to that which would occur at the death of a married partner.
Have it all down and agreed in writing
A will details what you wish to happen to everything you own when you die - they're not expensive and it's easy to draw one up. A simple straight forward will can be done using a self help kit, if it's more complex then you need a professional will writer.
Not only do wills make things clear between the two of you, but also to your respective families - the worst legacy anyone can leave their loved ones is a dispute over their estate when they're gone.
Make a cohabitation agreement
When you have sorted out all of the financial issues between you it's a good idea to pull the whole thing together with a cohabitation agreement. This stops you from arguing about these matters again and if things get difficult at a later date and the dispute ends up in court the cohabitation agreement at least gives you some facts to argue about rather than nebulous accusations!