I am a little curious as to how plus ones work, and who you are obligated to extend them to. I understand that obviously friends who are engaged, married, or in long term (or otherwise serious) relationships obviously have their SO invited, but what about friends who are constantly in and out of relationships? One of my close friends assumes she's getting a plus one, but the trouble is, she has had three "boyfriends" in the past three months. I don't want to make her feel as though her SO doesn't deem an invitation, but our mutual friends (who are single) are now thinking (and have voiced) that they will also be extended plus ones because they might get a boyfriend at some point prior to the wedding. I clearly don't want to exclude the SO of someone who is in a committed relationship, but at what point do you determine the relationship serious enough that you know you won't have paid for a slot that no one will take? Please feel free to take me to the cleaners if I'm out of line in asking this question, but I've only ever been to one wedding, so I don't know the rules for invites and the like. Any advice would be greatly appreciated. Thanks!