I know that it's just the way most of us feel about sexual loyalty, but WHY do we feel that way? I think it's paradoxical – on the one hand we have no problems having sex just for the fun and pleasure of it with people we don't love, but on the other hand, as soon we are in a relationship, we feel like sex and love are inseparable things. When you're being "cheated on", you feel like your partner does not really love you, because "if he/she loved me, he/she would only want to sleep with me". Isn't that weird? Why don't we think "yes, my partner slept with somebody else, but that does not mean he/she loves that person, just like I do not love every person I have ever slept with". Or why don't we think "No, I would never sleep with anyone I don't love, because then sex would be less meaningful once I'm in a relationship".