Praise be to Allah.
Undoubtedly, deliberately looking at women – especially those who are adorned – is something prohibited, and the prohibition is even more emphasised during the month of Ramadan, because sin is graver if it is committed at a time or place of special virtue, as has been explained previously in the answer to question no. 38213.
This haraam looking weakens faith in one’s heart, undermines the fast and decreases the reward, but the fast is not rendered invalid by that. The one who is committing this sin must hasten to repent.
Shaykh Ibn Baaz (may Allah have mercy on him) said:
It is haraam for him to look at women, and if he looks with desire, then the prohibition is even more emphasised, because Allah, may He be glorified, says (interpretation of the meaning):
“Tell the believing men to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts, etc.). That is purer for them...”
Letting the gaze wander freely is one of the causes of falling into immorality. What is required is to lower the gaze and beware of that which may lead to temptation, but the fast is not rendered invalid if no maniy is emitted. However, the one who ejaculates renders his fast invalid and must make up that day, if it was an obligatory fast.
End quote from Majmoo‘ Fataawa Ibn Baaz (15/269)
See also the answer to question no. 37654
What this husband must do is fear Allah and lower his gaze, avoiding looking at that which Allah has prohibited, and he should advise his relatives not to mix freely and explain to them the evil and bad consequences of doing so.
What the wife must do is remind her husband of Allah, and not delay advising him if she sees him committing some evil deed.
Undoubtedly heedlessness concerning the commands of Allah – especially in Ramadan – may expose one to the wrath and punishment of Allah, and cause one to waste one’s time during the season of goodness and worship on things that are not pleasing to the Most Gracious, may He be glorified and exalted. That is sufficient loss.
Fasting has only been prescribed so that people may attain piety, as Allah, may He be exalted, says (interpretation of the meaning):
“O you who believe! Observing As-Saum (the fasting) is prescribed for you as it was prescribed for those before you, that you may become Al-Muttaqoon (the pious)”
We do not know of any specific punishment for this sin in the hereafter; rather it is one of the minor lapses that people are prone to, and it is more likely to be pardoned on condition that one does not persist in it, and that one regularly offers prayers on time and avoids major sins.
And Allah knows best.