I'm going to ruin my friends relationship
What is your reason for wanting to ruin your friends relationship?
No reason, I just feel like doing it.
Your friend is not going to be happy if you decide to ruin their relationship. If you think that their relationship is toxic, then this is something you should tell your friend. If you break their relationship up then your friend will not learn anything from the situation aside from not feeling like they cant trust you.
Nah. Life is not too short to worry about being trusted.
Well, if you can't be trusted by your friend, then you are acting like you're not really their friend and they may end up resenting you and end your friendship. As we grow up, friendship can be harder to have so I suggest that you keep those that are close to you and make sure that you support them and help them during the times that they need you.