Lane… wasn't particularly shocked by the discovery. From what he knew, infidelity wasn't all that rare. His parents never cheated on each other, at least not as far as he was aware, but it still was a fairly common occurrence. Plenty of his classmates' parents had done that. And yes, it was bad, but such was life. People were frequently trash, and they hurt each other.
And it's not like Lane had any right to judge Austin. While he never cheated on anyone (which wasn't all that hard, to be honest, since his first and only romantic partner ever was Damien!), he had done… plenty of other terrible things. Such as stealing other people's lives, for example. He was doing it for a reason, yes, and he wouldn't do it if he had a better option… But he wasn't foolish enough to think that it justified him. That it would make a difference to all the people who got hurt by his actions. In the end, it was just a selfish pursuit of his own goals.
He was trash, yes.