Reading the last few pages, it feels like I'm the only one who just wants to see D & F in a happy, loving, all-girl harem without other men or animals involved.
You're by no means the only one, there's a lot of young people who react the same as you to the opening of D to other men. It's a matter of age! As I was a teenie myself or in my 20' I would have never thought of "sharing" my girl with other men. I was even jealous if she happened to have had a previous sexual relationship before me.. It's normal at that age. But people grow up.. get older.. see a lot of things.. change a lot of ways of seeing things..
At a certain age it becomes then also "normal" to have thoughts like: well.. this dear wife of mine was a virgin as i met her, I'm the first and only man in her life and this since .. many years.. I may have the biggest dick in the world but it's still only ONE dick, the same every day.. How does she feel about that? Would she maybe wish to try also other men? Just so .. for fun.. Does she miss that somehow? Would that maybe make her happier? Coz that's what I want above all, that she is happy!
And then you ask her, and start talking about it. Depending on her answer and how interested she is in this topic, you may then both decide to "open up" to other, non exclusive, sexual experiences. That can lead to joining a swinger community for instance or just live in an "open relationship" from then on. In full agreement on both sides and totally transparent, no lies no hiding.. According to some sources, this may even make the feelings between the 2 partners stronger! It's a kind of relation based on trust, truth and respect!
And you must agree, this solution for a long time relationships is much better than not talking about it at all and sooner or later find out that your wife cheated on you, or you start cheating on her, or both.. which does happen in real life in many cases because humans are simply NOT monogamous by nature!
Of course you may reply that D is still very young and their relationship is also very young so in this case things should not yet go in that direction. BUT.. Father is no teenager and he already has the "mature" idea of what real love should be. Not to mention that he sees clearly D's developments in terms of sensuality and sexuality, which in fact he induced himself, not to mention that he in fact cheated on her from the very beginning and he's not very proud of that..
Allowing her to open to other men would be only fair and then, if they have an "open relationship", he should also not have to hide his affairs anymore. Plus he would avoid this way that D, with her new discovered hornyness , may do some things behind his back sooner or later. That would be the end of their relationship, he could not love and trust her anymore if she cheated on him.
Taking all this into consideration, Father's decision to open D in this direction is the right one, even if D is still very young. But he's building for the future .. And she will of course follow his advices as she always does
On another note, you young people, already had 2 and a half chapters of D's exclusive relationship with her Father (and NO, lesbian scenes don't matter in the "exclusivity" with a man!) Apart from that, I BET you will always have the CHOICE to avoid any relation of D with another man also in the future, as you always had already till now. So what about you pick those choices and remain by your exclusive love story, but allow us, older pervs to also have our fun in the next chapters
Deal?
(see also my previous comments on this topic:
https://f95zone.to/threads/dating-my-daughter-ch-1-3-v0-26b-mrdots-games.597/post-3830632)