You can date anyone you want
No. She's a minor, you're an adult.
yes
yes it is, the legal age in Texas is 17 :)
no...
no
There are no laws regarding dating in Texas. There are laws regarding sexual contact, and he is taking a risk of being accused of illegal activity, even if nothing happens.
Yes
sure why not
yes
Yes
Absolutely not.
NO! And the 19 year old guy should go to jail if he has done anything sexual with the 15 year old girl!