Amber has spoken in the past about how they take pride in being open and honest, and therefore is more than happy about their arrangement.
I'm in my pajamas at 3 in the morning with my zit medicine on.
There are probably better cites to be found than the ones I added - I just picked the first relevant links that came up on Google, and the Sanger one in particular could do with improvement.
The reason behind their relationship coming to an end is because of the choice they made to keep their relationship open.