I've heard every single fucking excuse in the fucking book.
I didn't want to hurt you, so I lied.
I do need you around. You're just not what I need all the time.
We're no fun anymore.
I honestly couldn't give two craps about your cowardly excuse for why you would cheat. You did it. You are that person. Accept that, then maybe we can move on.
Except we can't move one, can we. Because you didn't accept that you're this person. The person who could systematically lie to the person you'd already managed to convince could trust you with everything they are.
You didn't just cheat on them. You broke them.
This scenario rings true for relationships of any maturity, and you could say that it's more acceptable in younger people. They're young, naive. They don't know that the things they do to another persons heart are going to keep them damaged and guarded for years to come. And by the same token, the other side doesn't know how to defend themselves against the damages done. They don't know to value trust and mutual respect, or that it is important to work hard at a relationship.
Having had these experiences young, however, they don't necessarily set you up for emotional maturity in a relationship when you're older. Especially when you're on the side that's being cheated on.
The very nature of a serious relationship means that you put more of yourself into it. You put in your safety, you put in everything you're afraid to lose. Because nothing could ever happen to it in the heart of someone who's promised to take care of it forever.
So when you, as a cheater, take all of that and lie and cheat, and you break that ever so important trust, you're a wanker.
But when you set about covering your tracks, and you start to project those vile characteristics you've developed within yourself onto your partner, you're so much more than a wanker. You, with malicious intent, start to emotionally break down another human being because you can't stand to face up to the simple fact that you've decided to not even try to work through why you feel this way. You've decided on whose feelings and whose heart is more important. You're a fucking coward.