If you must move from your unit for medial reasons, but your landlord will not let your out of your lease, your recourse depends on the state your live in. Landlord-tenant law is different in every state. Some states are more friendly to landlords, and others to renters.
First, try asking for some compassion from the landlord, given what you are going through. If the landlord doesn't behave like a human, then you may need to enlist legal counsel.
We can't speak to what the law says in your state, but in many cases, extenuating circumstances may allow him to terminate the lease.
If you are unable to come up with an agreement with your landlord, you may want to seek legal advice. There are legal aid offices in every state that help low-income persons. You can search for a legal aid office near you here.