Sandersonv is correct in the explanation of what an open relationship is (typically you are in a relationship with one person and the "open" part is purely sexual with other people), but I don't fully agree with her judgement that it doesn't work. If an open relationship is to be seriously taken into consideration, both partners must establish rules and follow them. Trust is key to making it work. If both partners want an open relationship, willingly participate in it and follow all of the outlined rules, it can work. But, and a big BUT it is, both partners want to have to look outside of their relationship for sexual release. It cannot be one-sided and work. Trust issues and jealousy cannot have any part in an open relationship, so if those exist, I then agree with Sandersonv that it wouldn't work.
An open relationship usually means that you and your partner are able to be with each other and other people at the same time... It doesn't work... Would you want to share your partner with someone else? Knowing they are with someone else, but they still come back to you? It's a fancy term for cheating on each other without the thought of getting caught and paying a consequence of losing your partner. Having your cake and eating it too. Bad idea.