Hmm. I think 'the 60's and 70's being quite bad in terms of infidelity' stems from people having sexual freedom for the first time ever, because of birth control, and because of the after-effects (psychologically) of the second world war - live for today and all that. Previously people would have been quite repressed sexually (in terms of the amount of people they were comfortable with shagging without serious repercussions, and the risks they were prepared to take.)
You have grown up in a very different cutlural environment to that. You have always felt free to take your pleasures wherever and whenever without stigma, shame or fear, because of those post-war shifts in attitude. They had some catching up to do - you do not!!!!
Lots and lots of relationships survive 'all kinds of shit' because these days marriage can last a very, very long time, and we all change, relationships and people change and evolve, go through peaks and troughs. But I'm quite sure the vast majority of marriages that have survived the 'shit' have done so because one party never actually finds out - or because of a guarded tolerance/indulgence of their partner's casual infidelities provided discretion is practised, a blind eye can be turned. An 'understanding' the way the French have (apparently) about taking lovers; not so much 'open' but tolerated and ignored, providing it doesn't threaten the status quo, and MOST IMPORTANTLY because they don't want or need complete honesty - having their nose rubbed in the lurid details of who, where, when, how. They just want their lives to carry on as normal, relatively unaffected. I imagine there are many more marriages surviving because of that, than because of the 'honest and open' way you are thinking of approaching things, which is quite a lot to swallow. (no pun intended.
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I think some people just know whether they have the kind of relationship that could carry the weight of all that knowledge, and others (most) know absolutely that they do not.
I'm not sure total honesty is always a very good thing. It's like you've dumped this information on your DH for him to try to digest emotionally, and saying you want to be unfaithful is practically like being unfaithful, but you can have a clear conscience because at least you've been honest. 
So what now? you say you'll never do anything he is unhappy about, but where does that leave you? And he is going to be wondering where the hell it leaves him if you say 'No, I categorically do not give you permission to do this.'
I hope you haven't opened Pandora's box. This is why marriage is hard. this is why it is what it is; a fantastic deal that comes with strict conditions. It's about sacrificing little bits of yourself for the ultimate good of the whole. I'm not sure it's possible to have it all, personally.