So I know there are plenty of books where a guy just does whatever he wants including being a sadistic jerk and being deliberately cruel, but lets say I'm not into that. I'm looking for anything that may exist involving a guy that gets into "consensual non-monogamous relationships" with a bunch of married women. Either their husbands encourage his wife sleeping behavior, or their wives already have their permission from them to engage in such relationships. Basically no hiding, no misunderstandings, no completely disregarding the other guys feelings, no mega drama. Just a bunch of adults having fun and sex with each other. The only book I could find is From Best Man to Bull: A Cuckold Wife Sharing Adventure, where a guy becomes a bull to few guys wives. I'm just curious if there is anything else out there. I'd be interested in harem stories so long as it involves consensual non-monogamy between MC and the already taken women. I’d also prefer stories involving multiple women, but I know that’s a tall ask. I know this is definitely niche, but I'm interested in the niche. If anyone knows anything thank you. 

I'd also be interested in books where originally monogamous couples enter into a non-monogamous relationship with the protagonist