Hmm. As far as a LI in general being
accepting of other women, that
is pretty much every harem game, true lol. But as far as 'official girlfriend' characters being like
"You can have all the side-pussy you want, I don't care, I'm yours! etc." then I can't say that I've seen it that often myself. The ones that I do recall are
Maureen (Timestamps), Jaime & Shauna (WVM), and possibly Robin (Mist), though I need to play more of it. Every now and then there will be one who can be convinced to accept another
specific LI, but not as often on this level, I've found.
But if you know of more than that then by all means please mention some! What bores you excites me and I'll gladly accept your rejects as recommendations!