Whats just inside of your line?

I wanted to make a thread the last time I had this conversation with someone but I waited and forgot, anyway the subject of discussion is what the the worst thing your best firend or girlfriend/ boyfriend could do to you that you would still be friends with them or in a relationship with them afterwards.
When you ask people whats over the line they generally go way over like murder and stuff so I started asking people whats inside their line to get more interesting answers.

Basically what the most fucked up thing you could forgive someone close to you for doing.