[R_Ellender]

1&2. If your opponent saw your hand, his optimal play would have been to raise, because he gains nothing by folding. This is especially true since you indicated in the beginning of your post that you planned on folding to a raise, so his raise had +EV.

Psychology is an extension of the Fundamental Theorem, as you'll learn later in TOP. If you only focus on the cards, then he played correctly by folding since your Q-high was probably best. If you factor in psychology, if your opponent knows how you play your hand(folding to a raise), raising becomes the correct play. His raise induces a mistake by you.

3. Yes, it would be correct to keep betting with the best hand, even if it was something as weak as Q-high. However, with a hand that weak, you're not really hoping for a call, since your bet is pretty much a semibluff. You should be satisfied with his fold, because a call on the flop may have caused you to play incorrectly on the turn and the river(if your opponent has nothing). You may be afraid to bet, and if you have the best hand, its clearly a mistake to give a free card.

As for the rest of your post, the summary of the chapter says it best. You should play the way that you would if you could see your opponents cards, simple as that. It's a general statement that takes into account everything from knowing what cards your opponent holds to knowing how he will play those cards(tendencies). When you analyze a poker play, you look at it from every angle to try and decide whether or not it was the optimal play in terms of +EV. You must take advantage of your opponents tendencies(folding too often, calling too much with bad odds) while not allowing him to take advantage of yours(folding if raised when you held Q-high earlier).