All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If the marriage contract was completed according to the Sharee'ah, then it is not invalidated unless the husband delivers divorce deliberately and willingly, or a Muslim judge issues the ruling of divorce for some genuine reason that are regarded in the Sharee'ah.
Therefore, if you had divorced your wife or that the Muslim judge issued the ruling of divorce and the waiting period of your wife has expired, then the divorce is effective and your wife becomes a non-Mahram woman for you. So, you are not permitted to look at her, or stay with her in seclusion, or even talk with her except for a necessity.
If you have not divorced her and the Muslim judge did not issue the ruling of divorce, then the marriage contract is still valid and she is still considered your wife.
As for your saying "I am not a practicing Muslim" it is totally wrong because Islam means submitting oneself to Allaah. In other words, a Muslim means the one who follows the Commands of Allaah and the commands of the Messenger of Allaah and avoids whatever Allaah and His Messenger forbade. Allah Says (what means):{So stand (ask Allaah to make) you (Muhammad SAW) firm and straight (on the religion of Islamic Monotheism) as you are commanded and those (your companions) who turn in repentance (unto Allaah) with you, and transgress not (Allaah's legal limits). Verily, He is All-Seer of what you do.}[Quran 11:112].
So, you should fear Allaah and follow the rulings of the Islamic Sharee'ah.
Know that merely pronouncing La Ilaha Illa Allaah will not benefit you on the Day of Judgement unless you act according to it.
Allah Says (what means): {Allaah will say: "This is a Day on which the truthful will profit from their truth: theirs are Gardens under which rivers flow (in Paradise) - they shall abide therein forever. Allaah is pleased with them and they with Him. That is the great success (Paradise).}[Quran 5:119].
We ask Allaah to guide you to the right path.
Allaah Knows best.