All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
It is forbidden for this husband to describe the physical features of this woman, if it is confirmed that he did so. Such behaviour could lead to a bad marital relationship and bad suspicion between the spouses. Indeed all means which lead a man to be tempted by a woman are forbidden in Islam. The Prophet said: ''A woman should not describe another woman to her husband as if he is looking at her.'' [Al-Bukhari]. The scholars stated that this is in order to prevent the husband from being attached to her and thus being tempted by her. This is in case someone else describes a woman to him, so what about himself describing the woman, which could be due to having looked at her and so forth? Therefore, this husband should be advised to fear Allaah and stop doing this.
We did not understand what you meant by saying that he lusts for her. If he meant that he wants to marry her, then Allaah permitted a man to marry up to four wives provided he is able to be just between them; but he should not mention this wish to his wife if he knows that such a statement would hurt her, especially if he is not very serious about the matter. However, if he meant, by saying so, that he lusts to do something forbidden with her, then this is evil, because wishing to commit adultery is a kind of committing adultery. The Prophet said: ''The child of Adam has to have his share of Zina (adultery or fornication) no matter how well he/she endeavours to avoid it. The Zina of the eyes is by gazing, the Zina of the ears is by listening, the Zina of the tongue is by talking, the Zina of the hands is by touching, the Zina of the foot is by walking [to forbidden places], and the heart desires and wishes. Then, the private parts either submit to this or deny it." [Muslim]. All the above acts were called Zina because they are a means to it.
Finally, it should be noted that the misbehaviour of the husband is not an excuse for the wife to refuse sexual intercourse with him. The Prophet said: "If a husband calls his wife to bed (to have sexual intercourse with her) and she refuses, and he goes to bed angry with her, the angels will curse her until she gets up in the morning." [Al-Bukhari and Muslim]. So, you should advise him in a soft manner and with good words, and beautify yourself to him so that he does not become attached to other women.
Allaah Knows best.