What is the ruling on adopting the view of Ibn Taymiyyah regarding a man who falsely swore an oath of divorce, knowing that he had illicit relationships before marriage?

You should not have asked your husband about his past, for what matters is his current state. It is enough that he has repented and become righteous. Praiseworthy jealousy is that which does not transgress the Sacred Law. As for swearing by divorce falsely, there is a difference of opinion regarding it. The majority of scholars hold that it takes effect, while Ibn Taymiyyah holds that it does not. You may adopt the view of Ibn Taymiyyah if you are a scholar and his opinion seems more preponderant to you, or if you are a layperson and someone you trust in knowledge and religiosity has given you a fatwa based on it. However, it is not permissible to adopt it merely to follow concessions. According to the majority opinion that divorce takes effect, if this was not the third divorce, your husband can take you back without a new contract as long as you are within the iddah (waiting period); otherwise, it would require a new contract after its expiration.