The first point I'll grant you, though if given a choice I'd undo the death of an uncle who I saw but a few times a year (who died at 50) over undoing all the bad breakups of my life and the reasons for them. Maybe that's unusual of me, but the fact remains that from my viewpoint, it's really, not the same when somebody hurts you and dumps you vs. when somebody is taken from you, and the latter hurts for much longer.
For the rest, though, no. You're taking my sentences out of one context and then trying to claim they're in another. That's gotten you a few mod points, but it doesn't actually address the point I was making in those sentences at all. The point was, in case you somehow failed to read the first sentence of the paragraph you're quoting from, that " humans aren't really wired very well for monogamy". They get away from it when they can, either by being powerful, or with the consent of their partners, or without that consent. I am by no means attempting to claim that these are morally equal, any more than I'm claiming you should look up to the powerful and vicious (which are *not* the same thing, though viciousness, like non-monogamy, is a thing that power can let you get away with and this appeals to many more people than you seem to realize). I'm not justifying a behavior, I'm simply highlighting the fact that it happens, and if society doesn't want it to happen the bad way (cheating) they need to legitimize it happening the good way (socially acceptable ethical polyamory).
As for my "ridiculous strawman", that's actually one of the core advantages of polyamory. Monogamous relationships require a tremendous commitment, not only to give up all the other relationships and partners you might have had, but to be there for your partner for whatever ey expect a partner to provide. Polyamory frees you from both obligations, allowing you and your partner(s) to get everything that is desired from as many sources as it takes. Of course, in practice it doesn't work out perfectly, but a lot of polycules can get closer to that ideal than the typical monogamous relationship.
As for your last argument, I disagree. I'm not going to touch murder, except to point out you've hardly argued that it's not inevitably part of human society. Back on topic, though, cheating *is* inevitable, so long as society requires people to give up a relationship before starting a new one (and accept a huge stigma in the process), but sneaking around without your partner's knowledge is still frequently possible. Adjust the latter and you'll get less cheating, though you'll probably still get some because people are bad at weighing consequences, especially when their hormones are up. Adjust the former, and the rate of cheating will go *way* down, because the only reason to do it will be because you want to hurt your partner even though you don't want to leave them, and that's a really silly reason (especially if separations are made easy and relatively effortless).