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Have you read your state landlord tenant laws? If not, you'll find them linked in the first "sticky" on this forum and you should read up on how to address maintenance issues and what your recourses are if the failure to perform them results in the unit being uninhabitable.
Humidity in the house and resultant mold aren't in and of themselves grounds for breaking your lease. Yes, of course you can break your lease. If your lease has an early termination clause you can utilize that or, if in your state a landlord has to make every effort to mitigate his damages by finding another tenant, you can reduce your own damages by those means.
There are laws concerning the return of your security deposit when you vacate the premises and you'll find these explained in the landlord tenant laws too. Any deductions from your security deposit have to be documented and itemized by the LL. I think you'll find your state laws very helpful. Good luck!