I completed deferred adjudication probation for felony assault, it wasn't even my girlfriend or wife, I was at a party and reacted to someone pulling a knife on me but it was initially seen by a female DA and female Judge as me attacking a woman, ...
As others here have said, you are probably eligible to purchase a firearm. You may or may not be eligible to obtain a license to carry depending on how much time has passed since you completed probation successfully.
Texas Government Code Chapter 411, Subchapter H covers the License to Carry a Handgun. Under Section 411.172(3) a person is eligible for a license to carry a handgun if they, among other criteria, have not been convicted of a felony. In order to know what "convicted" means you must look to the definitions listed under Section 411.171 of the the Government Code.
Section 411.171(4) states that:
(4) "Convicted" means an adjudication of guilt or, except as provided in Section 411.1711, an order of deferred adjudication entered against a person by a court of competent jurisdiction whether or not the imposition of the sentence is subsequently probated and the person is discharged from community supervision. The term does not include an adjudication of guilt or an order of deferred adjudication that has been subsequently:
(B) pardoned under the authority of a state or federal official; or
(C) otherwise vacated, set aside, annulled, invalidated, voided, or sealed under any state or federal law.
While the statute explicitly includes deferred adjudication as a conviction and thus prohibition against obtaining a license to carry, section 411.1711 of the Government Code also allows for the possibility for some people who successfully complete a felony deferred adjudication to apply for a license to carry if it has been more than ten years from the date of an order of deferred adjudication entered against them.See question