2) Do you say "This very well exemplifies why you are alone" or "This exemplifies very well why you are alone"? neither? Neither of them. You could use them, but they sound odd. - "And that's why you're alone" - "That's probably why you're alone/single (if they're complaining about not having a gf/bf)" If you want to sound well versed, you could say "Therein lies your problem" 3)Finally, does it sound odd to say "These muffins are my wife's and mine" And "These are your friend's and yours"? No. Yes, it sounds odd. But for the sake of clarity it often must be said that way, and even native English speakers will feel odd saying it - whether they admit it or not. 4) Do you say "Historic buildings/monuments/sites/architecture " or "Historical buildings/monuments/sites/architecture The former (the first one). But you would say Historical documents - for some odd reason.

Look up 'historic' and 'historical' in the dictionary; it clearly explains the difference.

As far as using they when you actual mean a gender neutral singular pronoun. Yes. It's not "grammatically" correct, but I do that all the time when I'm talking about a hypothetical situation. For instance: P1: What do you say if someone asks you for your number but you don't want to give it? P2: Why are they asking for your number? P1: They don't say. They just out right ask for your number. P2: Don't give it to them

"Now, you are always pulling that kind of stunt on me, aren't you?" Honestly, yeah, it would sound a little odd. I'd probably say one of the following: "You're always doing stuff like this." "Up to your usual antics!"/"Up to your antics, as usual!" This sounds more flirty and funny, as if you're in a good mood "Have you always gotta pull a stunt like this?"