Basically this, since it's an h-game and the MC is pulling a Heel-Face-Turn from an Ugly Bastard to Hentai Protagonist. The only thing in-universe that would raise his power levels even further would be if he got a haircut that obscured his eyes.
Slightly more realistically...exclusivity doesn't mean the same thing to men and women. For men, it's fear of paternity fraud and wasting resources on someone else's nut. It's a necessity in all but a few circumstances. For women, exclusivity is about getting as much attention and resources out of a guy as she can; if 10% of the MC's attention makes her feel twice as good and gives her a life twice as fulfilling as a guy who's loyal, she's going to stay and share.
If the MC slings dick like a Netorare Antagonist, rizzes them like a Hentai Protagonist, pulls in crazy earnings with that potion business, and manages (because plot) to be there for them whenever they need him, then he's not really going to have any competition. Few men can compete with that kind of FrankenChad. Which means, rather than ditch him for some random guy they can monopolize, the girls in his life would try to thin the harem instead. And, as you pointed out, the MC can handle that infighting by whipping out his hammer and nailing the problems.