If your girlfriend took a significant sum of money from you with the understanding it was a loan for a house, and has now refused to marry you or repay the funds, you may have legal options. While a criminal case for cheating (IPC 406/420) might be difficult if the money was voluntarily given, a civil suit for recovery of the money is generally maintainable. The success of any action will depend on the specific circumstances and your ability to prove the intent behind the transfer.