Hello Moonglow Gal,
Welcome to our forum.
I'm sure you'll have a lot of reading, conversing, and pondering to do before you decide whether an open relationship is right for you. A bit about terminology, "open" usually means that the "core relationship" is open to dating (and sex) outside that relationship, whereas in a closed relationship, there's no sex except inside the core relationship (although a newcomer may become part of that core relationship in due time). Non-monogamy refers to any situation where one has romantic encounters/involvements beyond the traditional monogamous "couple," whether those encounters/involvements are physical (sexual), emotional, or both. If it's both, then it's called "polyamory." Those are all real basic versions of the definitions ... Semantics can develop into quite a discussion among polyamorists.
Anyway, the best (or at least fastest, LOL) way to learn about polyamory (and open relationships) is to jump right in and start conversing with polyamorists. So you're in the right place! Check out the threads that interest you, start your own new threads if you desire, and make your thoughts/concerns/questions known. Polyamory.com is quite a busy site, so don't get discouraged if you get lost in the shuffle at first. Actually, chances are you'll quickly get responses to your posts, and find yourself making new friends.
I personally "fell into" polyamory ... via falling in love with someone who was already married. But I'd already gone through huge changes in how I viewed life and the world ...
You may find yourself going through huge changes too. But don't be alarmed if it turns out to be a gradual process. Actually, in the beginning, slow is usually the best way to go.
I hope you'll enjoy your stay with us.