I don't think the conclusions Marshall comes to are all that strange. You have to consider:
1) Marshall and the Duke don't know each other that well, so he doesn't know the Duke is an overly honest himbo
2)the Duke basically gave a single line summary of past events that made them sound more scandalous than they actually were
3)No brother wants to hear what sounds like his sister's sexual experiences
4)the Duke accidentally poked at all of Marshall's weak spots and insecurities during that chess match
with all the points I still say "they are still engaged" - they marry and he can't stop it. and she agree to get angaged with the duke by the way, no one force her. and has much the bro does not want to hear about his sister "sexual activity", I think it mostly his imagination then what the duke said.
the bro points of attacking the duke to be is cause "they not married" is just so dumb. at least he should use a different excuse to be angry other then his sister is a virgin and should not be with man. it just weird at this point ╮(￣▽￣)╭ the bro is just too weird
Marshall was upset because of the way the Duke was speaking about it. He interpreted it as his sister being disrespected. Even the mom interpreted what the Duke said as talking about sex. They were both shocked about it, if you'll recall. Like, what kind of guy says ambiguous stuff like that in front of his fiancee's family? The audience knows the true circumstances, but the family can only go off what the Duke says. And the Duke is the primary creator of misunderstandings.
Yes, you're right the Duke and Valerie are engaged and their business is their business. That's why Marshall didn't have a good comeback after the Duke said that.
I agree the duke did say weird stuff but again, the way the whole family jump on perv stuff right away from what he said is just....weird ╮(￣▽￣)╭ like really, how they jump to that kinda of stuff? from that point I come to the conclusion that this family is all perverted with dirty mind. so it's not really the duke fault, yeas he is dumb and say weird stuff, but I don't think it is his fault they have dirty minds
god the little bro logic is soo weird and out of this world（￣へ￣）he have so little sense I just can't take him seriously at all. he always forget that his sister is fucking Engaged!! how is that not important?
even the duke weird conclusion make much more sense then the little bro logic sense. the story become a mass, I don't know if I keep reading unless the little bro will go away from the story