At the risk of shocking people I will say that I don't see any problem with such a situation.
I used to know a guy and a gal, both friends of mine, who had the same arrangment. They lived it pretty well AFAIK. It took me time to get used to it though. There was a difference anyway, for their "arrangment" was coming into play when either of them was in a
bad mood.
I'm a very pragmatic person
*e* come to think about it, I wonder
why that gal even told you about it. You should ask her clearly.