I know K is just trolling but if he uses the word "sin" it's not so much about documentation and validation by the State, but more "in the eyes of 'God'" type thang.
As to me, and to answer the third question you asked, I felt that marriage was a more significant bond in that it is more tangible, real and binding than simply repeating "I wuv you" ad nauseam. I've had this discussion many, many times with many people, none of whom were married, so I was content to say "You don't know what you're talking about and wouldn't unless you tried it too, which you wouldn't, so let's agree to disagree". The state can get fucked and burn in hell (I come from Italy, cue the circus music now) - it's about the ceremony and celebrating your love for each other with your family and loved ones. Also wearing a wedding ring makes me look cool and mature and repels Thai hookers magnificently so it's quite a nifty gadget. It also has a small dent in it (it's 23 carat gold so is still very malleable) from when I punched a guy in the face for belittling my wife, which I find very poignant :D
Hmm. Well, I am engaged and we do plan to have the ceremony at some point. But, it's kind of the same already...in that we have some sort of formal (between us...in the sense that we formally agreed to be each others) and told like all our friends and family. She asked me to marry her, so she owes me an engorgement ring...nyah...I'm kidding there, I'm not that materialistic. I do have a symbolic item from her. It's that anchor thing, there's a pic in the sex toy thread of me getting pin wheeled, and it's in that. But I instead a wear a ring that was a gift from a former Officer Commanding, who says he got from someone else, an OLD TIMER, who took it from a dead German. It has the German Eagle and Iron Cross on it. For some tl;dr reason, that ring sort of became our relationship/status/blah ring for me. It's kind of weird, but it works for us. (And I still need to get her an engagement ring cause well, I have a job and she's a student.

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But yeah, I understand the ceremony aspect. I just don't get why sharing affection, love and closeness before that ceremony is wrong. I know Kaywholed is trolling...I was trying to troll back with somewhat Socratic questioning approach.
I kicked the shit out of someone one time for the same thing. She was not even with me, I was with a group of random dudes, and we where talking about our girls etc. He started talking smack on the grounds of a) the fact she is small/thin and has an A cup etc. b) that she is so sexually aggressive and dominant...basically calling her an ugly bitch and a whore.
So, I suddenly brought my big heavy boot HARD along his shin and into his ankle where it meets his foot. I felt a nice *crunch* under my boot, heard a wailing scream and he went down. (presumably, I dislocated or broke his ankle) then booted him the ribs as hard as I could 3 or 4 times and took off. So, I guess I admit that I'm protective of her to the point that I'll smash someone for talking bad about her...I'd hate to see what I'd do if someone physically hurt her... I don't even think I could watch her subbing to someone, not even to a hot girl. As soon as I seen her wince or heard a little cry of pain...I'd slide a 10 inch blade into the person at the pubic bone and pull up til I got to the nap of their neck.
I dunno...maybe if the person was REALLY hot, and we knew her and had a lot of trust and Ms.G really wanted to do it, I'd be able to relax and enjoy it. But no subbing to another guy. It's a little too intimate in the psychological/emotional way for my comfort. Domming, ok, if I'm there too.