Well, I'd be happy to just have one love in my life, but I suppose that if both partners agree to the polyamarity, it's ok. Each to his own. But from your post, it seems that you are not comfortable with the idea of being polyamorous, of having to share the love in your love with someone else.
I suppose swinging isn't that bad, as long as it is made clear to both partners that there is a strong division between the physical act of copulation, and the deep spiritual love that two people have for each other. I'd be more jealous if my girlfriend was having a mental, spiritual relationship with another man than if she was just using him for casual sex. Although it's easy to say that now, I'd probably be saying something different now if I had any relationship experience.
I find it weird that the brutal, physical act of copulation has been so closely tied to emotional love. I mean, sure, sex looks like fun, but all it is doing is releasing endorphins in the brain, it's nothing anything overly spiritual (I think, although I could be wrong).
Although, what is spirituality? What's 'real' love? Instinct? A chemical release in the brain?