Do you have any plans on refining the sex mechanic? To explain it's a little disjointed how the enemy(s) engage in it, sort of stepping over each other's toes or passively watching even when they're the only participant. Additionally even if you break free before a climax you still end up in the cum-covered state, and finally it just seems odd to me that Mezz climaxing would end the interaction in which any enemy is dominating them.
In general the battle sex mechanics are an attempt to approximate an actual dynamic scene. You don't get to see it all, but you can kind of fill in the gaps. Because of this "approximation" framing, it's never going to be perfect, though I try to coax what I can out of it. Believe it or not, a lot of time was spent just getting it to be as "coherent" as it is now: persistent cum was a huge thing to implement, bunch of extra art variants and checks, and there's a LOT in the system you don't see just playing it: things like a backoff timer so they don't immediately grab you again the moment you recover, a lot of finetuning of timing and chance for various things.
All that said, yes, it's still not a perfect "state simulation" of what's actually supposed to be happening (though the current version is a lot better than the early ones). This is partially the engine's fault: I like to joke that in RPGMaker, things that should be hard are easy, and things that should be easy are hard. You have to engage in a lot of...creative solutions to get the battle engine to do some of these things without becoming a total mess. But in general: yes it could be better, and I hope to fine tune more as I go with chapter 2. Potentially backporting some of those changes to 1 eventually. To give more specifics on what you asked about though:
-As far as "stepping on toes," I don't track a literal sex action state for each enemy, because doing so wouldn't be practical. I'm pretty happy with the idea they're just taking turns at random, rather than specifically tracking which is doing what at any given time.
-That behavior with one enemy should probably be patched, yes, and that shouldn't be too hard a change. In general the model I'm going off of is that once Mezz is being fucked in combat, every enemy either uses their turn to join in, or sits on the sidelines, and I'm pretty happy with that model. But if there's only one enemy left and he grabs Mezz, I should probably just do a check so there are no "waiting" actions.
-"if you break free before a climax you still end w/ cum". I think this came down to me dreading adding yet another state to track for Mezz in the additional battle engine I was building on top of the real one. I have a nude, no cum sprite sheet. It was probably also a case of "will people really care about how consistent this all is?" Well, now I have at least one data point that says they do, so I'll look into patching this into chapter 2 at some point.
-On climaxing ending the interaction, you have to see each sex cycle as kind of a mini battle within the larger battle. The boar's goal is to down Mezz, and normally they do this by reaching climax, but if Mezz is horny enough he downs himself mid-fuck. This is a "punishment" for him mechanically, because he has to start the cycle all over again, and he takes a health hit (health in CS isn't literal health so much as "ability to keep fighting"). The idea essentially is that Mezz climaxing during sex means the enemies get a "free turn" with him. It isn't a perfect metaphor, but I'm happy enough with it for now. I may do any number of things with the lust mechanic in general in chapter 2, including just scrapping it to make space for other things, so we'll see on this one.
So two yes, and two no.