"My husband is kissing another woman? I'm gonna get back at him by devouring the dick of a man I met only a few days ago. No, you can't blame me, I was drunk!"
The scene itself is well done, the alcohol helped her focus on Leon giving her pleasure that Alan just couldn't - but that wasn't my direct issue.
The problem is the aftermath: Clara wakes up in a panic, realizes she did actually cheat on Alan, tells Leon to forget their night ever happened and almost happily skips over to Alan and has a normal conversation with him. As if she didn't just cheat on her husband over a simple kiss. There is no discernible regret on her part, that little part of her conscience telling her she has crossed some lines she can never come back from again.