I have just been in that position.
We brought a house, I paid the 14000 deposit. The total bills and mortgage came to 1100 a month, I paid 900 she paid 200.
Six years on, because we did not draw up an agreement, she is entitled to half what the property is worth, minus half the mortgage.
This means she was entitled to 1/2 MY deposit too.
Look into how the house is held, there are 2 types, tenants in common, and another one I cannot remember. One means you get your deposit back, the other means that everything is halved !!!!!!