I've been needing to get this off my chest for a bit.
What do you need to get off your chest?
Can I be really honest here and tell you?
It is good to get things off your chest every once in a while. It isn't healthy to hold onto issues until they affect you.
I've been cheating on my partner with her best friend.
While I appreciate you confiding in me, I need to tell you your behavior is inappropriate. It is wrong to cheat on your partner and you should stop it immediately.