This is the 10467th most frequent Turkish word.
boşandığı
"Boşandığı" means "that he/she divorced" or "whom he/she divorced."
Here, 'boşandığı' is used as the participle form of 'boşanmak' (to get divorced), modifying 'year' to specify the time of his divorce.
O, geçen yıl boşandığı için yeni bir hayata başladı.
He started a new life because he got divorced last year.
In this sentence, 'boşandığı' forms a relative clause, specifying 'the person' whom the friend divorced.
Arkadaşımın boşandığı kişi şehirden taşındı.
The person my friend got divorced from moved out of the city.
'Boşandığı' in this context indicates the specific action of divorcing, directly relating to 'day' as the time.