I feel that I am being wrongly evicted from our apartment by another roommate who claims to be the only one on the lease. I'm pretty sure I signed it, too, but I can't remember. We moved in together and we've lived here for the last year and a half.
The first thing to do is to get a copy of that lease. Start with the landlord, who probably has a copy (and state law may require him to give you a copy if you request it). If you're on the lease, your roommate cannot get you out -- only landlords can evict tenants.
Now, suppose you're not on the lease. All is not lost. If the landlord has treated you as a tenant -- by accepting rent directly, for example, or putting your name on the mailbox or doorbell -- you may have attained the status of a tenant. Surely, if you and the roommate rented the place together and it was clear that you were on equal footing, you should be given the status of a tenant.
Once you are a tenant, a co-tenant such as your roommate cannot evict you. Only the landlord can do that.