How do I understand 「わが身世にふる ながめせし間に」

Question

This might be a difficult question but let me give it a try here.

I have trouble understanding this poem by 小野小町:

花の色は　うつりにけりな　いたづらに　わが身世にふる　ながめせし間に

I understand that the words 「ふる」 and 「ながめ」 are 掛詞, which means that they have two-folded meanings. In particular 「ふる」 can mean 「降る」 and 「経る」, and 「ながめ」 can mean 「眺め」 or 「長雨」. But I am not sure how to put them together in a grammatically correct way. In particular, I want to ask the following:

1. Is 「身世」 a single word, or are they two different words?
2. If they are two different words, then which verb goes with 「わが身」? Is it 「ふる」 or 「せし」?
3. Is it correct that I understand 「せし」 as 「していた」 in modern Japanese?
4. When 掛詞 are present, is it okay to expect the poem to be grammatically "correct" for both of its meanings?

P.S. I asked a similar question on a Japanese website. If you feel like answering it in Japanese, please follow this link.

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Problem solved: Based on @l'électeur and other people's answers, I'd say that this problem has been solved. Please let me summarize what I've learned:

1. 「身」and「世」belong to separate words.
2. 「我が身」goes with the word 「ふる」. When 「ふる」 is interpreted as 「経る」, which is the 連体形 of the 下二段 verb 「経（ふ）」 meaning "pass by" or "get old", the whole phrase 「我が身世にふる」 serves as a noun phrase. And it can be expanded into 「我が身が世にふるのを」. I failed to see this because のを is absent from the poem.
3. 「眺め」is a noun, which becomes 「眺めす」, a サ変 verb, when combined with 「す」. This verb means to absent-mindedly gaze at things. The form 「眺めせし」can be understood as 「眺めていた」 in modern Japanese. (This was pointed out by a guy at the Japanese site that I alluded to in my question.)
4. It is generally not reasonable to expect complete grammatical correctness for both meanings of the 掛詞. For example, when 「ふる」 and 「ながめ」are interpreted as 「降る」 and 「長雨」, the grammar becomes pretty sloppy here.

P.S. Any further points are still welcome through the comments.

Answer 1

1) Is 「身世」　a single word, or are they two different words?

Two separate words.

「わが身{み}」 is the first-person pronoun.

「世{よ}」 means "the/this world".

　

2) If they are two different words, then which verb goes with 「わが身」? Is it 「ふる」 or 「せし」?

It goes primarily with 「ふる」 and secondarily with 「ながめせし」.

"got old while gazing"

3) Is it correct that I understand 「せし」as 「していた」　in modern Japanese?

Yes, it is 「した」 or 「していた」 depending on the context.

4) When 掛詞{かけことば} are present, is it okay to expect the poem to be grammatically "correct" for both of its meanings?

No, it is not okay. 掛詞 are only word plays. You would need to be just playful and imaginative with them. You would often wind up getting disappointed if you analyzed the grammar used around 掛詞 too seriously.