As you grow older, you realize there are people around you whom you cannot fathom. Probably, you just brush it aside as, ahh s/he is just being dramatic, or s/he is just craving for attention when you were younger. That may or may not be more acceptable. When you're young, everything you do, is more acceptable.
Not when you're older, or rather, much older. People expect you to be more matured, to be more realistic, to be more logical, and not act like a total idiot.
As a guy/girl, you don't go liking every single person out there that you encounter with. I don't call this immature. I call this being an idiot and desperado.
Regardless of the status of that person, you like him/her, being close to that person, only to regret later on and proudly brag about this? This is something you should be shameful of. Perhaps, this person is trying to victimize him/herself. Few months later, only to find yourself going to that path again.
My friend or not, this is someone I look down to. It doesn't matter if that other married party was the one initiating it, but you know you shouldn't be breaking people's family apart. It takes 2 to tango. You are wrong, it really just means you're wrong. You can say you are not wrong, if one insists, what can others say. It's still morally and socially wrong.
If single people don't like you, it means just one thing. There's something really wrong with you. If it's just one, two, three, or four, I can register. But, if it happens all the time, it's probably the attitude problem. If one is desperate, it's quite easy to tell. If you come off as a despo, you can't blame people for not liking you. People don't like a despo.
The quote "being classy is not about being stuck up. You need to cultivate respect for everyone, including yourself" is so right.