If my fiancé and I have lived toghether for 2 years but now we are splitting up, since she wants me to leave do I have to be legally evicted?

Who has legal possession of the place where you live, and do you pay rent or are on a lease?

1) If your finance owns the home or is the tenant and you do not pay rent to either the landlord (if she has a landlord) or to her, you are a guest, not a tenant. She can ask you to leave at any time, without prior notice or warning. If you do not leave, she cannot simply lock you out, but can immediately bring an "ejectment" action in court to remove you--ejectment is essential eviction for non-tenants.

2) If you both own the property, neither can make the other leave, though it may be  possible to get a court order requiring the property to be sold and the proceeds of the sale divided according to your relative ownership interests.

3) If you are both on the lease together from the landlord, she cannot make you leave--only the landlord can evict you, and only for good cause (e.g. nonpayment; destruction of property; disturbring the peace; etc.).

4) If you rent from your fiance, then--

a) If there is no lease, you are a month to month tenant or subtenant  of hers, and she can give you 30 days notice terminating your tenancy, then  bring an eviction action if you won't go.

b) If there is a written lease, she can only evict you for good cause (nonpayment, etc.) or as provided for in the lease, or when the lease expires.