[iapr]

I think the real question you need to be asking yourself is are you really ready to be married and committed to one person or is what you are interpreting as "possibly joining the lifestyle" really more about just wanting to bang more chicks? The two are completely different and it is a valid question.

Swinging is something that a happily committed couple does as part of their sexual dynamic as a couple. Being a free man and being able to come and go as you please and to invite into your bed whoever you please is a completly different reality and the two do NOT mix.

When I was 40 and had been faithfully married for ten years and had kids and a mortgage and balancing two careers and wanted explore different sexual options with my wife as a couple, I became interested in "joining the lifestyle."
When I was 23 I wanted to bang chicks.

Banging chicks is about freedom and owing nothing to nobody. Swinging is still about committment.

Your real issue here isn't about how to approach your GF about swinging. Your first real question should be to yourself if you are really ready for committment or if you are still wanting to sow some wild oats.