Is it against the law for a parent to enroll an 18-year-old in school without their consent in Houston Texas?

It may not be against the law - most states allow students to withdrawl at 16 years of age. It is a good idea to stay in school though. No matter how bad it is right now, you'll set the tone for the rest of your life if you drop out. You'll never go back, and at best you'll have a GED. You'll find later that it may be something your ashamed of, and it will be difficult to get into college. Your financial future rides on this decision - and that of your future family. Don't cheat your children of financial security because you made mistakes at a young age. Finish school - it can only help you.