I kind of hate how MC"s either have a small dick , or are a weakling. Or the fact alot of MC's are super into the fetish right away without talking it over much or easing into it slowly.
1st part just simply change the MC and how he acts. 2nd part make the MC have actual conversations about it with his wife or girlfriend more often than one time. Tho I do understand why the 2nd part isn't done very much as dev's are solo usually. So they want to speed the process up for the sake of not taking to long to get to the good parts.
I'm entirely with you. When the MC is set up that way, mentally, emotionally, physically or all three, I'm immediately out. That is not what I'm here for and its not sexy at all to me.
And to the second part YES, so much yes. For it to be sexy and arousing in this type of situation, for me the MC needs to gradually come around to the idea over time. Or else some sudden, life changing catalyst that sparks a quick move into sharing for both of them. But when games or stories have the MC being the one who's pushing her into having sex with other men, especially when he's not getting it on with any other women himself, its just weak and pathetic.