Not sure if you have this or not but give it a look.
Texas property code
Scroll down to page 539 that's where Landlord Tenant starts.
I cannot speak to Texas, in most jurisdictions if an annual lease was signed and not renewed it goes to month to month. All the terms of that original lease still hold.
Yes, 30 days notice is needed (some places it's 60 days) if you choose to not lease the unit to them. As for a reason when ask I would simply state that I am choosing not to rent it at this time. This avoids personal feelings and he said she said scenario's. Besides you don't want to give a reason that could give them wiggle room. Less is more here.
If I were in your situation I would be serving a Notice to vacate, as you did. I would make sure that you served it correctly per the law. This starts the clock.
As for the Baby Daddy as you refer to him, there will be a law, (in my lease I use 5 days) as to how many consecutive nights your client can have a guess. Once he has pass that time she is in violation and you may precede with eviction. On a Month to Month the eviction will take longer and you have the burden of proof.
I would simply over look, but document the guess staying pass the allotted time. I would serve her notice per the law that you will not be renewing her month to month lease and she will have to vacate. The manner in which you serve this notice is EXTREMELY important as when she doesn't vacate you will immediately move to evict and it will be based on her being served the notice to vacate. Some jurisdictions want you to certify mail it, some want you to post it to the front door. Some want both, some want specific information given. The process will be in the law link above or by visiting the courts.
It's never a bad idea to visit with an attorney. I would find one that works for a flat rate as oppose to an hourly.
Above all else never lose your composure. This is business and you are to act and be professional at ALL times. (Even though you want to kick them in the as* and send them on their way)