Questions & Answers about Я хочу честно признаться другу, что я устал.
Другу is the dative case of друг (friend).
The verb признаться (to confess / admit to someone) is constructed with:
- the person you confess to in the dative:
- признаться другу – to confess to a friend
- признаться маме – to confess to mom
- what you confess is either:
- a clause with что: признаться другу, что устал
- or a noun in the prepositional with в: признаться другу в ошибке (to admit a mistake)
If you used друга (accusative), it would suggest the friend is a direct object, but признаться doesn’t take the person as a direct object; it takes them as an indirect object, so you need the dative: другу.