If your former girlfriend was someone that you at any point had lived with and/or had a child in common, then assaulting her would make out the elements of a misdemeanor crime of domestic violence under Federal law. Here's how the definition reads in part from 18 USC 1921:
A “misdemeanor crime of domestic violence” is an offense that:
(1) is a misdemeanor under Federal, State, or Tribal law;
(2) has, as an element, the use or attempted use of physical force, or the threatened use of a deadly weapon; and
(3) was committed by a current or former spouse, parent, or guardian of the victim, by a person with whom the victim shares a child in common, by a person who is cohabiting with or has cohabited with the victim as a spouse, parent, or guardian, or by a person similarly situated to a spouse, parent, or guardian of the victim.
Under the Violence Against Women's Act and the Lautenberg Amendment, a domestic violence conviction takes away your Federal Second Amendment rights for life. There is no way to restore the loss of these rights at this time, which means that even if Texas were to grant you gun rights, you would be unable to pass a NICs check and could be subject to a Federal prosecution if found by the Feds to be in possession of a firearm.
As to the felony, under both Texas and Federal law, a deferred adjudication would be considered a conviction for purposes of firearm rights, but at least that could be rectified on a state level. If you can get the case expunged -- which would first require a pardon from your governor -- you could get your state rights back. Lautenberg, however, would still bar restoration of your Federal rights IF your crime conformed to the Federal definition I gave you above.
So in brief, presently you have no gun rights. If you assault did not involve someone you lived or had a child with, a pardon from your governor would get you your state and Federal rights back. Otherwise, you have lost your Federal rights for life until such time as the law changes.