[Sashimister]

Originally Posted by Columbine

That is so useful to know! I have never understood the use of くwith an adjective. My teacher gave us the impression it was just an aesthetics thing and never even mentioned it modified verbs!

Being a mere Shinjuku wino, I shouldn't be criticizing a teacher but that's never an aesthetic thing. To modify a verb, one has no choice but to conjugate the adjective to end in く. It has nothing to do with aesthetics or personal preference.

Ok, i know it's horribly complex and if it's going to be a pain, please don't feel obliged to answer, but how do you tell that 自分 is the girl? Because of the previous sentence? 自分 is a nasty word for Japanese-learners because we're told it means 'yourself, myself' and we're given examples of it using it from our own perspective　（このテブルを自分で作った etc）. Then later you find out it's used to talk about other people, and when other people are talking about third parties, and it's just so muddled people generally stop using it altogether because it's too easy to get it wrong. At least, that's my experience of 自分.

You can tell that 自分 is the girl from the context. Presumably, the speaker wouldn't attend 一高の運動会 (He lives far from Tokyo) or know well 秋元子爵の令息.

You also need to look at the preceding sentence carefully. だが或る時、彼女は真面目になつて話をした. Its subject is 彼女.

The next sentence (the sentence in question) doesn't have a subject and it isn't even hidden (omitted) as in many Japanese sentences. This is because it's NOT a sentence, so it doesn't have a verb, either. It's only a noun phrase ending in こと.

「ずつと前から、自分は一高の運動会やその他の機 会で、秋元子爵の令息をよく知つてること。」

Think of it this way as one sentence:
だが或る時、彼女は真面目になつて話をした that ずつと前から、自分は一高の運動会やその他の機 会で、秋元子爵の令息をよく知つてる

自分 is a nasty word, I know. One needs patience to learn it. Who it refers to depends on the context.
このテーブルを自分で作った。 me
このテーブルを自分で作ったの？ you
自分でつくるカレーが一番おいしい。 anyone who makes curry
時間がないの。自分でやってよ。 you
えっ？時間ないの？じゃあ自分でやる。 me
スミスは自分の家で仕事をしている。 Smith
窓ガラスを割った人は自分から言いなさい。 whoever that broke the window

One clue would be to carefully look at the verb and think who does/did/will do the action.

I had dictionary issues on that one... so 私の方でも好加減に、華族の息子としてふるまつて居た would be "even though I did so halfheartedly, I behaved as though I were the son of some nobleman."

Exactly.

I'm still a little stuck on しまひには. I think しまひ must be 姉妹 but the には. I ~want~ to put something like "Because of the sisters (conviction), it couldn't be helped, and even though-" but to me には doesn't seem like a 'because'.

Major mistake there. しまひ＝しまい＝ an end. しまひには= at the end, finally.
Had it meant "sisters", the word would have been written in kanji as has already been earlier in the essay.

Have you not heard phrases like 「今日はこれでおしまいにしましょう。= Let's call it a day now.」?

The pronunciation is different between these two words, too.　Highest pitch in red.　
姉妹　＝　しまい
しまい　＝　しまい

"On the small paths of the cicada ringing forest, basking in the summer twilight, with the girl my quiet acquaintance, it seemed like she would open up completely and reveal whatever secret was in her heart"?

Much better but I'm still unsure as to how you got "with the girl my quiet acquaintance".

「かなかな蝉の鳴いてる森の小路で、夏の夕景を背に浴 び ながら、女はそつと私に近づき、胸の秘密を打ち明けよ うとする様子が見えた。」

様子が見えた tells us that what's said here occured only in the speaker's imagination. It was his faint expectation.

"On the small ......... twilight, I was able to see the scene where the girl would come near me quietly and tell me the secret of her heart."