Completely up to you. I know some people that have a month or two in-between each time, and others that like to wake up to it and end the day with it. There isn't really an 'average', every person or pair is different.
Also, less sex does not equal an unhealthy relationship. Lots doesn't mean it's healthy either. It's something to figure out with the person you'll be with, and if you both respect how each other feel about how often you'd like it to be, you could find something you're both comfortable with.