Does a husband's diminishing sexual desire for his wife, despite their love and his lack of interest in other women, indicate that he has been bound from her, and is it sufficient to recite verses for undoing ties over water, without using lote tree (sidr) or bathing with it, to undo this tie?

What happened to your husband might be a magical binding from sorcerers to cause separation between you, or an organic or psychological sexual weakness. Therefore, it is advisable to consult doctors and adhere to ruqyah (definition) (Islamic exorcism). You can also seek help from trustworthy scholars experienced in ruqyah. One must be patient with tribulations and content with Allah's decree, for there is great reward in it, and the tribulation might elevate one's status.