Is the legally described seclusion considered as the husband having entered his wife, and accordingly, does the wife become forbidden to her husband after he has divorced her three times?

If the husband consults a trustworthy scholar and truthfully recounts what happened, then you may act upon his fatwa. For the layman, who does not derive rulings, it is obligatory for him to ask the most knowledgeable and trustworthy in matters of his religion.

If a husband divorces his wife three times before consummation, she becomes irrevocably separated from him by the first pronouncement, and the remaining two pronouncements do not take effect.

The issue of whether seclusion (al-khalwah) takes the ruling of consummation (ad-dukhool) is a matter of disagreement among jurists. According to Imam Al-Shafi'i in his new opinion, seclusion does not carry the ruling of consummation, and therefore its rulings do not apply, nor does divorce pronounced during it take effect.

In summary, it is incumbent upon both spouses to strive for family stability, and for each to fulfill the rights of the other and treat them with kindness.