The statute does in fact contain a loophole, an affirmative defense, allowing for consensual sexual activity for children 15 years or older with an adult no more than 3 years older than the child.
Please don't be fooled into thinking that when you turn 16 and your girlfriend is 19 that you are now within the protection of that affirmative defense. The State of Texas CAN strictly construe that 3 year difference to mean a 36 month difference between the day your girlfriend was born and the day you were born. If she is so much as one hour older than those 36 months the State of Texas can proceed with charges against her based on the type of sexual relations you engaged in.
If she is outside of that loophole and you engage in consensual sexual activity with your loved one she may be charged with Sexual Assault, a Second Degree felony that carries with it a punishment range of 2 - 20 years in prison, a fine not to exceed $10,000 and registration as a sex offender for a ten year period after she serves her timein prison. And she can get that punishment for each and every time the two of you engage in sexual conduct.
I have defended over 50 cases of Aggravated Sexual Assault, Sexual Assault, and Indeceny with a Child and trust me when I say its not fair to your girlfriend. Its not worth the risk if she is older than you by more than 36 months.
What you do is between you and her, but if you love her and care about HER best interest, you'll protect her from your desires and hers.
Best of luck.
Criminal Defense Lawyer
Bennett & Hernandez
Criminal Defense Lawyers