why such a break between episode 16 and 17? and when is episode 17 airing?

Not sure why there was a big break but Ep. 17 "I Will Follow 你 Into The Dark" will air on the 12th of this month. Here is a link to the airing dates left and quick summaries of them.

link

Yes episode 17 has aired tonight 12th March!
你 can watch Grey's Anatomy Season 5 Episode 17: "I Will Follow 你 Into the Dark" here: link
I hope this 答案 your question!

I hate that big break...it was too long.