I received an eviction notice from my girlfriend. I paid her $500 to $700 a month to help
With household expenses. I am not her tenant, no contract and she asked me to move in. What can I do to stop this?

First, your girlfriend didn't give you an eviction notice but a vacate notice. Only a court can issue an eviction order. A vacate notice is the first step in getting an eviction.

Second, you ARE her tenant. She is either the owner of the property or the leaseholder. Either way you have an agreement with her to live there. The agreement may only be oral, but it exists nonetheless.

So, since there is no lease, you are a month to month tenant. As such she can terminate that tenancy at any time with proper notice. What proper notice is depends on where you live. But I suspect she researched it. She give you written notice to vacate and how long do you have?

But if she wants you out there is nothing you can do to prevent it as long as she follows the rules.

Agree, yes you are her tenant, she either owns or has the lease on the property. You helping her does not put you on her rental agreement or lease.

She will be able to evict you if she no longer wants you in the home.