I get the idea that he wasn't clear on what being open or poly actually entails, which meant he wasn't able to voice his expectations. That, coupled with him not being able to pick up on your end of things--the condoms were an obvious indication of your thoughts--resulted in the gears grinding. I'm a bit puzzled as to why he seems to think it's somehow all your fault and that you cheated on him, though.
That notion of you cheating when you'd already agreed to being open and fucking other people suggests that he's either still thinking of being open in terms of monogamy (it's monogamy with fantasies of threesomes enabled!) or he's far more insecure and territorial than he thought he was (or so goes my hallucination on the matter). Neither of those is insurmountable.
And it may be a case of him simply not having a large enough pool of potential dates so that he feels some equality in the arrangement. To that, I'd simply say he needs to grow up a bit--life isn't fair--and simply wait until you get out of Dodge and get somewhere with more people. It could all be tied to him also being stuck in the backwaters of Kansas instead of in a metropolitan area and he's just not comfortable in general...which will also pass when you finish business where you are and move.
Shoot, Wichita is likely close enough for him to find a variety of potential dates without distance being much of a factor.
And should you need to spend time venting to a face across a table in a coffee shop, we're here in KC. Heck, Curly can even provide a pretty face for that sort of thing.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.