The emotion that beautiful things gave me was wonderful, but I could neither hold onto it nor repeat it forever. Even the most beautiful things in the world eventually bored me.
Literal
Beautiful things [subject-が] giving feeling [topic-は] wonderful was [but-が] me [to-には] that feeling [object-を] holding thing [also-も] forever repeating thing [also-も] could-not. World [possessive-の] most beautiful things [even-でさえも] finally me [object-を] bored [copula-のである].
A long, literary meditation on beauty's transience. 感動を保持する事も、いつまでも繰り返す事もできなかった uses parallel も...も...できなかった ('could neither X nor Y'). でさえも means 'even.' 退屈させてしまった uses the causative ('made me bored') + てしまう (completion). のである closes formally.