Couples who are in open relationships accept and allow each other to date or have sex with other people. It means they are honest with their partners about sleeping with other people and ideally don't see it as a hindrance to their relationship.
There are different reasons why couples might agree to open relationships. Some people really believe in loving more than one person at the same time. Some are looking for the closeness of a steady relationship without giving up the thrill of new sexual experiences with other people. For others it could be because of lack of sexual compatibility, or living far away from each other. Or maybe they’d really prefer to split up, but because of circumstances – children, family, money – they choose to stay together but have other relationships too.
There are couples who find open relationships work out well for them. But many run into problems. It seems like an appealing idea at first, and you think you’ll be able to cope with the emotions. But in reality there’s no avoiding it: you end up feeling jealous. This can damage the whole relationship.
The best thing to do before entering into an open relationship is to have a long talk about it and share your concerns and insecurities. Then it might be good to test the waters by trying how it works for an agreed period of time before you make the final decision.