grammar - Ending sentences with the て form

I have a question pertaining to the following line in a manga.

いや実【じつ】は最近【さいきん】下【した】の名前【なまえ】で呼【よ】び合【あ】う事【こと】になってよ

The speaker just called his girlfriend by her first name, and this surprises someone. That person then asks about it, and the speaker is explaining it to that person.

What confuses me is the て form ending the sentence. What would be the difference between 「なって」 and 「なった」 here?

I am fairly confident that this is not a request or command. If something is being omitted, I am not sure what it could be.

There have been other circumstances, though never in formal written material. In conversation, are sentences perhaps occasionally ended in the て form out of carelessness?

I would appreciate any help understanding this.

Answer

It's not so much by carelessness as constructive intention or sense. It keeps the sentence unfinished and can attract the listener's attention by making him/her wonder what happens then.

However, in this case, I guess what's omitted here is what the speaker said before the example sentence, in short, the te form stands for causal relationship between the omitted part, which should be the preceding remark.