unless you marry only the court of equity could possibly give you an interest in the house, Lloyds Bank v Rossett [1991] 1 AC 107 indicated that this would only happen in two situations;
1) Express agreement, arrangement or understanding, plus detrimental reliance on that agreement
2) Where courts Imply common intention evidenced by direct contributions to purchase price (e.g. paying the mortgage directly), in which case you would recieve a share in proportion to the amount you put into the mortgage.
this is a really simplified version of what would happen but you should assume that you will not get anything out of the property if you split up without either paying the mortgage or with some sort of agreement to that fact.
good luck