OT: Open Sexuality?

So last night I was talking to Andres about threesomes because Jack and I were debating whether they ruin relationships or not. I believe that they do because I am pretty conservative with sexual relationships, in a sense that I sleep with 1 person at a time and when I'm in a relationship I only sleep with that 1 person. However, Andres brought up a point about being open to talk about sex. He says especially 10 years or so down the line in the relationship, there comes a time when the couple gets tired of having sex with each other.

What he's trying to say is that when the relationship becomes more established and that the trust that is placed between the couple is strong enough, talking about having sex with other people should be ok. In other words, sex and the relationship should be viewed separately.

I disagreed with him completely because when it comes to being in such a committed relationship, especially with 10 years down the road, I am conservative. I don't think that having sex with other people should be even an option. If sex gets to a point where the couple get tired and bored of each other then there is already an issue. Sex has everything to do with intimacy and the relationship as a whole. How can you simply have sex with someone else and expect to come home to your partner as if nothing happened? I mean yes, your lover knows and in a sense approves of sex with other people but physically I would feel different. Also, it damages one's confidence in bed. Am I simply not good enough?

Those are my reasons for why I'm insecure about having open sexual relations 10 years down the line in a relationship. Actually, it is not insecurity because I'm am secure but it's more about not knowing how I would feel about you after you sleep with someone else. I understand the things you do in the relationship and how you show that you love someone but sex is also an expression of that love and the fact that you might need to have sex with someone else eventually in the relationship just damages that expression into tainted empty words.