I'm a landlord so I can only offer this from my viewpoint. And this gets into some gray areas. I'm not condemning or condoning anything, just pointing out some scenarios.

First, most states (and I'm inclined to think yours does too) requires 30 days notice minimum to vacate the premises for breaches of contract other than non-payment of rent. If they fail to vacate, tenant can be evicted after the 30 day mark. In my state if the reason for Notice to Vacate is non-payment of rent I'm only required to give 10 days and if tenant fails to leave then evict (eviction process that takes 30-45 days in my local court).

Technically if you initiate the breach of contract, such as leaving prior to your lease expiration, or some activity that is a breach, you are responsible for rent for the term of your lease ~or~ until the place is re-rented.

However, here is the primary area I see where it gets gray. The Manager probably was not following the law when he told you to leave "immediately". In addition, he should have done this process in writing. So even though you breached the lease by allowing another party to reside there without them being on the lease (registered offender or not), the Mgr in all likelihood did not follow legal procedure on his end. A court might say had he given you 30 days notice as required by law, he could have used that time to secure a new tenant, and possibly re-rented in time so that he did not lose further rents.

In addition, one cannot necessarily be evicted soley because they are a registered sex offender.

The example/quote below pertains to Iowa law and evicting registered offenders:
As a landlord, if I find out that a sex offender is renting property from me, can I evict him/her?

A landlord may begin an eviction proceeding in court for a number of reasons:

The landlord chooses not to renew the lease, and the tenant refuses to vacate.

1. The landlord rents month-to-month, and gives the tenant notice to vacate at least 30 days before the next month's rent is due.
2. Non-payment of rent.
3. The tenant has violated the lease.
4. If the tenant poses a clear and present danger. This would have to include the tenant committing an act, or threatening to commit an act, that would cause harm to a tenant or the landlord; or committing an act, or threatening to commit an act that would cause harm to someone either on or within 1,000 feet of the rental property.

 Landlords may not evict a tenant based solely on the fact that s/he is a registered sex offender, without one of the above factors applying.

So for that reason, I'm not sure how it would hold up in court if he decides to pursue it, since he probably wasn't following the law himself.

I do understand your landlord's perspective as well, though. It's a situation that requires diligence, especially if an offender is convicted of crimes against children and there are children in the vicinity. If something were to happen... As an aside, most but not all registered offenders are convicted of crimes against minors. What falls under that category varies by state code. For instance, in Connecticut, being convicted of Public Indecency, defined by penal code Sec. 53a-186 will result in being listed in the registered sex offender database.

So you need to check your state's landlord tenant statutes. Google it like this (without quotes) "Texas landlord tenant law" or "New York landlord tenant statute". Everything hinges on your state's landlord/tenant laws and what your lease stipulates.