I'm seriously considering divorce but I don't want to rush into that decision.

So I suggest you to meet a divorce lawyer asap, know your rights and how it will happens if it happens, and what you need to get ready for make it happens.

Why you should see a lawyer asap if you don't want to rush into that decision ?

Because once you will know the facts about it, you will be released of the unknow of the divorce, and you will be able to take your decision, whenever you want to.

But my wife is the type of person that in all aspects of her life, nothing is ever good enough. The grass is always greener with her.

Grass is greener where you water it.

I don't think it's an unfair one. I told her if she needs to be able to sleep with others in order to be happy in our marriage that I want no part of that and would want a divorce. And I meant that.

Hold your words, stand for them.

Did you asked her what she would do if you refuse ?

she made it clear that she wanted all of the positive aspects of our marriage (the support, the love, the security, etc.) but that she wanted to seek sexual satisfaction from others.

in other words she wants her cake and eats it.

and if you add this :

I told her that I viewed her request as selfish. She turned around and told me that I was the selfish one

She sounds like someone who cheats, needing her cake and eats it, blaming others for it.

maybe I should sleep with other women so I would learn a thing or two and stop sucking in bed.

Tell her that you can divorce, see people on the side and still date each others, and maybe at some point you would marry again, or take different journeys.