What is the ruling on breaking an oath to abandon a sin, and is the questioner considered a non-Muslim after saying, "If I were to return to what I was, I would abandon the religion of Islam," and then she returned and then repented?

You made a grave mistake when you swore to leave the fold of Islam if you committed that sin. This does not result in disbelief or leaving the faith, but it is a great evil from which one must repent. You are also obliged to offer two expiations for these two oaths, because each of them is a binding oath. The expiation for an oath is feeding ten needy persons, or clothing them, or freeing a slave. If you are unable to do so, then fasting for three days, and it is more cautious for them to be consecutive. You must also repent to Allah Almighty for the sin you swore to abandon, regret committing it, and resolve not to return to it.