Another post rekindled my interest in Bertrand Russell. A man of many facets that definitely did not preclude love and sex.[switchonnow.com]
I do think a more mature approach to long-term relationships is due in western society, but I also think this is highly individual. I'm not sure I could ever stray, even with the understanding that extracurricular activity is permissible, but I wouldn't stand in the way of my partner if she wanted something on the side. I don't own her, after all, and she can maker her own decisions. Russell is opposed to casual sex and, for myself, so am I. But I think a lot of people successfully navigate casual sex, effectively separating deep and loving relationships from exciting sexual flings. If my partner felt the need to stray, I hope she'd be honest with me about it and take precautions to maintain our relationship as the primary. That might mean being careful to not develop a deeper connection with other men or women, keeping it somewhat casual. I understand what Russell means about not decoupling sex from love, but I think maybe there are ways to maintain a loving relationship with one person while satisfying other needs and desires with others.
@Lorajay "Comfortable" might be the wrong word for how I'd feel. I'd feel jealous and insecure, but at the same time she's an autonomous person who can decide for herself what's right. But I don't want her to hide anything from me. I think that's my one hard line: open and honest communication.
I agree that it depends on the individual and like you I'm a one at a time person. Unlike you i would not feel comfortable sharing.