Is it permissible for a husband to accept his wife's purchase of a house with an interest-based loan due to the unavailability of another option, while she refuses to move to a Muslim country and rejects his other religious advice, and what is the optimal action for the husband in this situation to preserve his religion and the upbringing of his son?

Firstly: It is forbidden to take out a loan with interest to buy a house, because the need for housing can be met by renting, and this is not a necessity that permits what is forbidden.

Secondly: If the wife insists on taking an interest-bearing loan, the sin is hers, and it is permissible to live in the house for the one who borrowed, provided that they repent. There is no harm for you in living with your wife in this house.

Thirdly: You should call your wife to uprightness and to abandon immodest display, and explain to her the rulings of Islamic law regarding modesty, seeking help from righteous people if available, and from materials that soften her heart.

Fourthly: A child is a trust and a responsibility upon his father, and it is obligatory to protect him, raise him, and shield him from corruption and deviation, based on the words of Allah Almighty: (O you who have believed, protect yourselves and your families from a Fire), and based on the words of the Prophet, peace and blessings be upon him: (All of you are shepherds and all of you are responsible for your flock). Be keen on raising your son and protecting him, and know that your staying with your wife and son is more beneficial for them, and you are responsible for both of them. Therefore, weigh the benefits against the harms.