Unfortunately you aren't entitled to anything. Regardless of whether you have been paying your half of the mortgage for 5 years or 20 years, you dont own any part of the house, however, you have just been paying rent.

Depending on what state you live in, you may be able to sue under a theory of "unjust enrichment." I agree with another poster that you have been essentially paying rent, but if the half of the mortgage you've paid has been in excess of what the fair market value of the rent had been, or if your paying half the rent has afforded your ex-fiancee to get a better place, the propery to appreciate and gain equity, etc., you may be entitled to a share of the financial windfall your ex has gotten. Again, depending on the state, your code may be similar to California's (Civil Code section 1590) - "Where either party to a contemplated marriage in this State makes a gift of money or property to the other on the basis or assumption that the marriage will take place, in the event that the donee refuses to enter into the marriage as contemplated or that it is given up by mutual consent, the donor may recover such gift or such part of its value as may, under all of the circumstances of the case, be found by a court or jury to be just." The catch is that the money paid for half the mortgage must have been in contemplation of the impending marriage, thinking that the two of you were investing in your joint home for the future. If he owned the house before you moved in and you just started chipping in for the mortgage, you might have a tougher uphill battle to show that it was under the assumption that it was in contemplation of getting married. Will you get everything you've paid back? Unlikely, even under the unjust enrichment theory. Part? Maybe, depending on the value of rent vs. what you paid. If we're talking a good chunk of money, it might be worth consulting an attorney.