On Tuesday, 13th of December Apple released OS X 10.12.2, as a security update. If you want to read more on the security problems with filevault that got fixed, read this article.
Since updating my computer, I was having problems with my ssh connections. Every time I connected, I had to fill in my passphrase. Very annoying, indeed. After some googling and trial and error, I found a solutiion.
Apparently OS X 10.12.2 changes tha way keys are used. And what most people tell about the problem is that the key needs to be added to keychain. But how to do this?
After reading this tutorial on adding an existing ssh key in os x, I figured out the steps, and I can confirm that this works:
First check which identities are loaded
Then load your identity
Finally check again which identities have been loaded, there should be one more in the list now.
This should be it, now you're ready to work again without typing or copying your passphrase on each ssh connection.