Is で marking end of the sentence in this case?

Question

I was struggling with this sentence from Yoshimoto Banana story called ミイラ

...それは普通のセックスで普通に気持ちいいというものではなくて、何か歪んだ喜びだった。

My translation: it was kind of perverted pleasure, (何か歪んだ喜びだった) it was ordinary sex (それは普通のセックスで) (but) it wasn’t ordinarily pleasant (普通に気持ちいいというものではなくて)

How can I tell if というものではなくて negates only 普通に気持ちいい or if it also negates それは普通のセックスで? (so the translation would be "it wasn’t ordinary sex) Would there be a comma? Or am I getting this completely wrong?

I know this is kind of confused! Thank you so much for any help!

Answer 1

You have parsed it wrong. That で in bold is not a copula (だ) but a simple case particle that marks a means/method/reason. 普通のセックスで here means "by/from (having) a normal sex".

それは［｛普通のセックスで普通に気持ちいい｝というもの］ではなくて、…

(Very literally: It was not an I-am-ordinarily-pleasant-by-having-an-ordinary-sex thing, but ...)

→ It was not an ordinary pleasure of an ordinary sex, but ...