I am a convicted sex offender (misdeanors plead guilty to in 2010). Is my landlord discriminating against me?

If your room-mate has the lease in his name and you are not on the lease, there may be a provision in the contract that does not allow for sub-letting. The landlord may have been putting up with you until he was made aware of your past troubles. In any case the landlord would not need an excuse to kick you out IF you are not on the lease and such a clause does exist.