From unethical to ethical.

I got into thinking the other day that how common it is for couples to start non monogamy not exactly ethical way? Something about me is that my first real relationship was a open one. But we were young and did not know how to define it. It was pretty much on and off long distance relationship and my then gf said to me that she thinks that it's ok for us to be physical with others when we're not together. To ehat i said "ok". And we had don't ask, don't tell policy about that. So to this day (22) years later i don't know if or what she did. I did not go further from kissing with anybody. And i think being poly or not monogamous has made sense to me all my life. I've told this to all my next partners in life but they have been very mono normative people and so i've lived monogamous relationship life after the first one. Fast forward to this day. My now gf has cheated on me several times. At least one time that i know of where sex was happening and several that i know where kissing was happening. We have talked about those situations and i have not reacted with anger. More like with understanding and compassion. I've told her about my views of openness and how it makes so much sense to me. She understands and i think mostly agrees with my views and i think is even curious about that life arrangement. And i offered her to open up officially and live a enm life. But she has not willing to that. I think she is afraid to loose me to someone else. But i already explained and give her reassurance and all. Now we haven't had a talk about it for months and i know she's doing borderland stuff with other men and women(and maybe even more). And even i had lately encounter with other woman who wanted to kiss with me and i let that happen. So I'm reading all the books and watch videos and listen podcasts about enm. And that got me thinking that how common it is to new polycurious people to start off with this lifestyle before becoming official and test the waters the non ethical ways. And if you're one of them, then how did it end up for you?