That is an open relationship. If it really is working out as well as you say it is, then you are a lucky man; most people can't handle that kind of relationship. Make sure you keep your eyes open, though, especially when you start having sex and when it comes time to end the relationship. Things might get touchy around then.
I think people tend to have the wrong idea about relationships. The participants usually end up being obsessive, clingy, and jealous, which, while being very unhealthy, is also human nature. As with all aspects of human nature, it is possible to overcome those feelings, but doing so takes a lot of self-discipline and is very rare.
I agree with Dan Savage when he says that we should no longer consider monogamy to be the most important requirement of a relationship.