it's a hairy subject. it just depends on the people. how secure they are with themselves and how their mind works. it's good when a couple has an equally strong and easy going possessivenes of each other. trust and SELF-assurance that you're mate isn't thinking of another person in an improper manner or witholding jokes, fun times, or feelings TO ME is very important. also when you're together with someone for a long time an emotional shorthand is created and you know exactly how far you "stray" from you're mate when hanging with friends. this all could be debated forever though. so many variables.