In order for a gift to be enforceable, three things must be present: (1) the donor's intent to give the ring as a gift, (2) the donor's delivery of the ring to the donee, and (3) the donee's acceptance of the ring. If you can demonstrate all three elements, a court will consider the ring to be a gift to you.
You will of course also have to prove that the ring had nothing to do with an engagement or marriage.
When it comes to engagement rings, Texas law applies the conditional-gift rule, which means that an engagement ring, by its very nature, is a conditional gift given in contemplation of marriage. The conditional gift rule as applied by Texas courts contains an element of fault. This means that Texas courts will look to which person is at fault for breaking the engagement.
From a practical standpoint, what all this means is that if a women accepts an engagement ring and sometime thereafter breaks the engagement for no justifying reason, the law requires her to return the ring to her former fiancé.
However, if you can disprove your ex's claim that the ring was an engagement ring, and prove the other 3 elements above, a court will likely find that the ring was simply a gift to you and can not be revoked.