An instructive loss

I see nothing in contrast to opening principles in my game however it was a quick execution of my king from my opponent.  

I actually preferred when you had the moves written out to this final diagram. That said, the problem is simply that "opening principles" are not enough. And actually, they should often be ignored.

This looks enough like a game I recently played (as White) I did a double take.

Bottom line is EVERY move you make in the opening should be towards emphasizing your advantages and/or working against his advantages. (Silman would call them imbalances). White pretty much did this. You didn't.

For example, You made a typical error people make when playing against the London system. You brought your dark Bishop to d6. He retreated his dark squared bishop to g3, and you mistakenly traded. This is exactly what people playing the London system want you to do. Every time this happens in a game of mine, I inwardly smile. It opens up the h file for what is potentially very dangerous monkey business by White. Black then needs to tread very carefully.

Your pawn moves weakened your position. His pawns are well positioned.

You castled into trouble, he did not castle (breaking a "rule") but leaving that rook on the beautiful open h file. That lack of castling by White also happens often in the London system.

The mistake with the exchange of bishops is typical of what people often do. They play exchanges without asking themselves who the exchange is going to favor. It doubled his pawn right. Yeah, but things like doubled pawns have upsides if you aren't careful. That doubled pawn ate your lunch. Often instead of exchanging, it is best to leave the tension on the board. While I don't know the specific position when the exchange was made, typically in the London system, it IS best to leave that tension be.

Here is that game I played recently with the same problematic bishop exchange and a similar bad end for Black.

 As an aside, 14. Qb1 on my part was not best. I should have just played Bxh7 right away.

To add to this, I might just add that these so called "rules", while providing some guidance for beginners, often need to be broken. For example, in both your game, and in the game I played shown above, white moves his dark squared bishop twice in the opening. This breaks the rule, "Don't move the same piece twice in the opening."

I would suggest reading the section on openings by Jeremy Silman in "The Amateurs Mind" for a more detailed exposition about what I am talking about.

Again, these rules are certainly something you want to consider. And they make a reasonable guidepost for starting out. But they do, and often will need to be broken to adjust to the realities of any given position.

That rule is all well and good, but here if white does not violate it, when Black takes the dark squared Bishop on f4, it does make a mess of the position w/o the compensation White gets with the open h file (if Black takes) when the Bishop retreats to g3. If Black doesn't take, then White still has the tension on that diagonal, and additional control over the e5 square.

When I look at the final position in your game, I struggle to come up with any kind of coherent plan that Black (you) had in dealing with the position. Instead, I see a lot of random stuff. You are playing for the center with the c5 push. Then you have the f5 pawn push that weakens your control of the center as much as it helps it. So while you go off pursuing different things, White has played in a coherent manner that has led to his ideas coming to fruition way before your ideas did. Blindly following is a great way for your King to end up in the morgue.