Can I evict my girlfriend, or boyfriend in Texas?

This depends on whether you have a written lease with the boyfriend or girlfriend. If they have signed a lease, they may only be evicted if they have materially breached the lease—and breaking your heart is not ordinarily a breach of a lease, much less a material one. If they signed a lease, and are in default (say for not paying rent), then the landlord can evict them as they would any other tenant in breach of a lease.

If there is no lease, the girlfriend or boyfriend is essentially a squatter. Texas does not permit "self-help" evictions, meaning that it is not permissible for you to change the locks and throw all their belongings on the lawn. You must go through the evictions process established by law.