Hubby and I agree that playing alone, particularly when it is more than just quick sex, has a thrill all its own - like dating. We have even gone separate ways on occasion for weekends or brought along our lover on a business trip or seminar in a nice location when the spouse couldn't make it. It's fun, but when the time is over we are ready, and it is so nice (and thrilling), to get back home.
It goes back to what I think is a human dichotomy - we all want the security of a home and a mate while wanting the thrill of the new sexual relations. Love and understanding in the first allows the second.
As for emotional bonds, they can develop, but that can be a good thing. Hubby says that if he were to get hit by a bus it is reassuring to know that Red would be there for me. And besides, I have varying emotional attachment to other people I don't sleep with, so that's not the issue.
Another reality about human nature is that mating for life is only a 50/50 likelihood even if a couple doesn't swing and believes in monogamy forever. Being able to satisfy the need for sexual variety in a loving marital relationship actually removes once reason for the big breakup.