Hmm, I really like the idea that D that date a girl less experienced (Or more beta) than D....
what if she got a young lady to be her gal Friday - perhaps in Chapter 4 as her career is blooming.
Any kind of relations of D with other GIRLS would be absolutely OK from my point of view. Even in a normal (not open) relationship in a game or in real life. Because a woman is not a man. A woman is in no way to be seen as "competition" for a man. She doesn't take the place of a man in the heart of a woman. She occupies the place of a WOMAN there, which is NOT MY place. A woman doesn't even have a cock lol so.. no "penis envy" either and.. absolutely no problem

. Be that just sexual or polyamory, I would have no problem sharing my "one and only" with anotherWOMAN.
Where I would have a problem though (be that in a game or in real life) would be if D (or her equivalent in RL) started another ROMANTIC relationship with another MAN. Sharing her sexually, for fun (hers and mine) would be OK but sharing her LOVE for me with another man .. hmmmm that's hard.. Because that man, unlike a woman, would really take MY place in her heart (or at least part of my place). Love is the base of our relation. It's what keeps us together it's what we have ABOVE all other things that we may do with others or not. It's the most valuable thing we both have. It's not just.. fun. That would mean indeed polyamory and I don't think i could share at that level.
And although such 3 some relations (1 man 2 women) that i called "mini harems" before would be indeed polyamory relations (sorry for using the wrong term) and I would have no problem with such relations, i don' t think i could accept a polyamory relation where another MAN is involved. Maybe if i was gay or bi (like in House of Cards lol) but I'm not.. After all, in a MFF relation the 2 women have also feelings for each other and enjoy each other also sexually (like Dee and Elena) so it is easier for each of them to also share the man they love with each other. But in a MMF relation that's not possible unless the man is gay or bi. Otherwise it wouldn't be "fair" for the man..
The only type of relationship where i would be able to accept a romantic relation of my beloved woman with another man would be one of the kind F/D/G/O. Which let's say started by simple "swinging" between 2 couples but developed with time into a polyamory relation where everybody loves everybody. The "fairness" of a "wife swapping" relation which is "i give you my wife, you give me yours, let's fuck!" could be transferred in such a case to a polyamory relation. And with that i could be OK. "I love your wife and she loves me and you love my wife and she loves you" That's still fair! I would lose half of the love of my wife but that half would be filled by the wife of the man who got that half.. And that goes for each of the 4 people involved. Fair deal! Therefore acceptable! And in such a case I wouldn't have to be gay or bi. I could just become best buddies with the other man. After all, we share the best we have lol..
I would really love to see a path like this and a corresponding ending in DMD. The only games that have such a path (and such an ending among others) are 2 of the Lesson of Passion games and Dreaming of Dana. I enjoyed that one but.. Dana was no Dee lol (and also no animations).