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```

    会ったのを今は後悔してる。
    
```

I was baffled as to what を was doing here. After some research, I figured it
could be a combination of nominalizer "の" and object marker "を," the action
being 後悔する. Is this understanding correct? If so, could I do either of the
following:

  1. Omit を
  2. Throw in お前を and so on to step up my syntactic confusion: お前を会ったのを今は後悔してるのなんだ！ ('Cuz I'm regretting having met ya!)

*I had trouble identifying を, since the verb was sort of concealed by its noun appearance. Additionally, with 今は in the way, it was all the more perplexing for me.
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2018-04-06T04:28:12.613
57750
2018-04-06T04:55:45.020
27674
question
syntax particle-を
Identifying the function of を here (as in のを)
> I figured it could be a combination of nominalizer "の" and object marker
> "を," the action being 後悔する

Your understanding is correct.

To break this down a little further:

`会ったの` is a noun meaning something along the lines of the English "having met
(you)" or "that I met you". We can reasonably assume the subject is the
speaker, and the object is probably the person that said speaker is speaking
to, although we would need more context to be sure of that.

`今は` means "now", but because this is a [contrastive
は](https://japanese.stackexchange.com/questions/46946/can-someone-explain-the-
contrastive-%E3%81%AF-to-me), the important thing here is that the speaker is
emphasizing that they regret meeting someone _now_ , as opposed to some
previous point in time when they didn't regret it.

`後悔してる` [後悔](http://jisho.org/search/%E5%BE%8C%E6%82%94) is a straightforward
する verb meaning regret, and the `してる` (`している`) just means that the speaker is
currently doing said regretting.

In short, if we assume the object of `会う` is the person being spoken to, the
sentence means:

> Now I'm regretting having met (you)

To answer your questions:

  1. In a lot of casual speech particles (including `を`) are dropped, but I assume that's not what you're asking. Grammatically, there's no basis for you to drop `を` here.
  2. You could make the object of `会った` explicit, but the correct particle is not `を`, it's `に`. It would be `お前に会ったのを`. 
  3. Incidentally, if you want to use `のだ` for emphasis/explanatory purposes, it would be `後悔してるんだ`, not `後悔してるのなんだ`, which is unnatural.
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2018-04-06T04:55:45.020
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2018-04-06T04:55:45.020
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answer