I have work 6 months with my boss bt he didn't...

We would like to inform you that if you mean that you want to terminate the work, then according to the UAE Labor Law states the below:
Article (116):
Where a contract is revoked by the worker for reasons other than those stipulated in Article (121), he shall be required to compensate the employer for any damage the latter sustains as a result, provided that the amount of compensation shall not exceed half a month wage for three months or for the remaining period of the contract, whichever is shorter, unless otherwise stipulated in the contract.
Therefore, if you want to terminate the work then you have to pay the visa expenses.