We're hardly free from Puritanism's bullshit. Monogamy is still going very, very strong. I mean I don't know about you in the UK, but over here in the US, the Puritan values are so ingrained in us that even amongst the atheists and "religious nones" there's still a lot of monogamy, and I don't just mean an aversion to cheating, or serial monogamy, but straight up cultural monogamy where being anything less than monogamous is practically discriminated against. You talk about not being monogamous at work and you're liable to lose your job, depending on where you work.
And it wasn't just men having fuck buddies, btw. Women did too. That said, I wouldn't call it Paganism to simply not be religious. Paganism is a collection of religions, and sure, a lot of them are way more free about sex than the Abrahamic ones, but you're not a Pagan simply because you don't care about religion. But I get your point obviously. But describing people who aren't Christian as "pagans" is literally a Christian concept so if you going around calling us all pagans you're furthering that philosophy.