As another reviewer mentioned, this isn't really a book about swinging, and it is really more just a book about two people who don't know where their lives are headed, and who are not really all that sure if they're going about fixing them in the right way.
That said, it does still feature a fair amount of sex and swinging, and it does get quite graphic in places (I almost felt it was a little too graphic at times); however, it is graphic in quite a casual, offhand, manner which manages to keep the book at a more serious level, and it seems the sex scenes are not really written with the intention of arousing the reader (although, that's not to say they are bland or boring).
I do think some people might find it a bit much, and for that reason it's not a book I'd recommend to everyone. I found it a really great and gripping read though, which stays fast paced and punchy throughout; it was one of those books that I found very hard to put down, with a great writing style, and well developed characters.