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.
Suffering from OCD is one of the afflictions with which Allaah tests His slaves; we implore Him to bless you with recovery. Indeed, He is The Healer, The Lord of the people, the Remover of trouble, none brings about healing but Him. So implore Allaah frequently, for He answers the supplications of whoever calls upon Him and relieves their distress; He says (what means): {Is He (not best) Who responds to the desperate one when he calls upon Him and removes evil and makes you inheritors of the earth? Is there a deity with Allaah? Little do you remember.} [Quran 27:62] For more information about treating OCD, please refer to fatwa 90425.
This action on part of this young man, if true, is a prohibited act. Some scholars even declared it a grave sin. Ibn Hajar Al-Haytami wrote, "The grave sin no. 387: peeping through a small hole into someone's house without his permission to spy on the women of his household..." [Az-Zawaajir] He cited many ahaadeeth, some of which were the following:
- Abu Hurayrah reported that the Prophet said, "He who peeps into the house of people without their consent, it is permissible for them to gouge his eye out."
- Anas ibn Maalik said, "A man peeped into one of the rooms of the Prophet. The Prophet got up, holding a blade. It is as if I am looking at him, about to stab the man."
- Sahl ibn Saʻd said, "A man peeped through a round hole into the dwelling place of the Prophet, while the Prophet was holding an iron comb with which he was scratching his head. The Prophet said, "Had I known that you were looking (through the hole), I would have stabbed your eye with it (i.e. the comb). Verily! The command to take permission to enter has been enjoined because of sight (that one should not look unlawfully at the state of others)."
All these ahaadeeth were cited in Saheeh Al-Bukhari, Saheeh Muslim and other books.
Hence, your cousin bears the sin, and there is no blame on you in this regard. So do not worry about that and repel any thoughts you have about it. Satan wants to disturb your life with such obsessive thoughts, so you should tease him by seeking refuge with Allaah from him, preoccupying yourself with reciting thikr, and totally disregarding his satanic whispers.
We could not find any statement of the scholars indicating that your cousin is liable to something for merely looking or attempting to look at your ʻawrah (body parts that should be concealed as per the sharee'ah). It is sufficient for him to secretly repent to Allaah of his sin. Hence, there is no point in forgiving him or not in this case.
Allaah knows best.