。
To tell the truth, I'm tired of it.
Literal
Truth [object-を] say [conditional-と] I [topic-は] that [target-に] got-tired.
本当を言うと ('to tell the truth') is a set phrase — literally 'if one says the truth.' A common conversation opener for confessions or admissions. 飽きた ('got tired/bored of') takes に for the object of boredom.