Can someone help me with this sentence?

[berrycarrier]

あなたずーっと握りしめてるんだもの
I roughly know what this translates to but I would appreciate if someone could break down the grammar within the sentence - particularly the end. The verb nigirishimeru is used but what is that ending? Is it te-form? xx thanks x p.s. its from Spirited Away in the first scene of the film.

 

[Haruto Uzumaki]

I'm not Japanese and I'm still kind of a beginner in the grand scheme of things, considering I've kinda been slacking but

「握りしめてる」→「握りしめている」 (in the current state of holding onto) in colloquial speech the 「い」 often gets dropped)

「ん」→「の」 (explanatory particle that indicates an explanation to something) in colloquial speech the の often becomes ん
「だ」→「である」 (「だ」 is essentially the casual version of 「です」, also formed from a shortening of 「である」)

and then in this case, as 「もの」 means "thing" I would personally translate 「だもの」 or 「だもん」 to something like "it's that..." (but I never formally learned this, I just assumed based on what I've known and the conversations I had)
so in total I would say something like "it's that I'm holding onto you forever"

and I checked with DeepL and I guess you shouldn't trust me at all I need context to be sure but I guess it's more like "it's that you've been holding onto it forever" but that could still be completely wrong so don't listen to me, just listen to the experts who will probably write a reply right below me... I just wanted to try out helping in this way but I'm used to conversations and not just isolated sentences

 

[berrycarrier]

I'm not Japanese and I'm still kind of a beginner in the grand scheme of things, considering I've kinda been slacking but

「握りしめてる」→「握りしめている」 (in the current state of holding onto) in colloquial speech the 「い」 often gets dropped)

「ん」→「の」 (explanatory particle that indicates an explanation to something) in colloquial speech the の often becomes ん
「だ」→「である」 (「だ」 is essentially the casual version of 「です」, also formed from a shortening of 「である」)

and then in this case, as 「もの」 means "thing" I would personally translate 「だもの」 or 「だもん」 to something like "it's that..." (but I never formally learned this, I just assumed based on what I've known and the conversations I had)
so in total I would say something like "it's that I'm holding onto you forever"

and I checked with DeepL and I guess you shouldn't trust me at all I need context to be sure but I guess it's more like "it's that you've been holding onto it forever" but that could still be completely wrong so don't listen to me, just listen to the experts who will probably write a reply right below me... I just wanted to try out helping in this way but I'm used to conversations and not just isolated sentences

yayy!! thank you this is really helpful! I had an idea of the translation so the grammar breakdown was extremely useful thank you so much <3

 

[Haruto Uzumaki]

Glad I could help at least somewhat I can at least parse sentences properly but I'm not the best person to take a final translation from

 

[Toritoribe]

もの/もん is a sentence ending particle for explanation or excuse. もの is often used by females.