退屈 and 飽きる: being bored and growing tired of something
Compare boredom at home with growing tired of a game played repeatedly. Preserve the book that prevents a long wait from being boring and the sunset one never tires of watching.
Boredom with 退屈 and the condition of having a book
退屈 (たいくつ) describes being bored or finding a situation tedious. In 「雨で外へ出られず、家で退屈していた。」, the speaker was bored at home because the rain prevented going outside.
「待ち時間が長くても、本があれば退屈しない。」 says that even a long wait is not boring if there is a book. Keep the condition 「本があれば」 together with the negative 「退屈しない」, rather than making long waits an unavoidable cause of boredom.
The repeated activity with 飽きる and a view one never tires of
飽きる (あきる) describes growing tired of a thing or activity. 「同じゲームを毎日していたら、さすがに飽きた。」 reports eventually growing tired of playing the same game every day.
「この丘から見る夕焼けは、何度眺めても飽きることがない。」 says that the speaker never tires of the sunset viewed from this hill, however often it is watched. Read the repetition in 「何度眺めても」 together with the negative 「飽きることがない」.
Duration and repetition are not absolute causes
Boredom at home and growing tired of the same game illustrate a present state and a change in response to repeated activity. Both expressions can concern boredom, so they should not be separated by a fixed boundary between short and long periods.
Having a book while waiting and repeatedly watching the sunset show why time or repetition alone cannot determine the feeling. Check each condition and negative before treating the examples as a general rule about becoming bored or tired of something.
Does the sunset example mean that watching it many times eventually becomes tiresome?
Show the answer and why
It says the opposite. 「何度眺めても飽きることがない」 means that the speaker does not tire of it however many times it is viewed. Preserve both the repeated viewing and the negative statement.