Nice comment, love all the directions you took with it.
In regards to girls getting hurt from cheating - In short, I believe it's better to manage a relationship well and set the correct frames honestly, but I also believe it's very important to 1. protect a girl from negative emotions, and 2. maintain the condition of the relationship. For this reason, I stand by my strategy to deny sleeping with other girls (at least proof, but you can always say that you're not the kind of guy who can only be with one woman).
In regards to eventual monogamy with a girl, I think this fine to have. My own time period for converting a non-monogamous relationship to pure monogamy would be 6-12 months after you start seeing each other, and the longer the better - because this allows NRE to wear off and you can see how well you two mesh together after that time.
It's definitely possible (and probable) that a girl will sleep with other men while she's new to non-monogamy. However, understand that 50% of women won't do it, and of the women that do, they usually do it to test your frame and see how you'll react. Women really don't like to sleep with lots of men, though (that's something we value as men) because women value commitment more. So, a girl will adopt whatever strategy she feels will help get her closer to monogamy, which also includes sleeping with other men to make her main guy jealous in the hopes that he will commit to her. Understand that just like you may throw out a frame that you're seeing other women (with no proof) she may ALSO give you the frame that she's exploring other guys (like having her tinder out, texting other men in front of you) with no proof, just to see what you'll do as a guy. This is also why it's best to be outcome independent, smile and don't give a shit about what she does. Instead, focus on being her best guy.
On letting a girl fuck other guys - I personally don't think there's anything more Alpha than telling your girlfriend that she's free to fuck other guys. The reason being is that it's the least needy frame you can ever take with a girl, and one that's also totally not possessive or jealous (meaning that as a man you have very little investment in her or what she does with her life), so all in all it's a good thing for your relationship. The big downside of course is that as a girl she's definitely going to test that frame by doing exactly that and then seeing how you react when she tells you that she fucked another guy. I have a recently new girlfriend that did exactly this - she first tried to sway me more to monogamy after I gave her the talk, and when that didn't work she is now trying the extreme opposite strategy, which is insinuating at having sexual adventures.
I think it's always better to sexually awaken a girl, because that's a stronger frame.
Hope this helps and keep us posted, man!