I'm going to fool around with my ex girlfriend/close friend's brother
Why would you fool around with her brother?
It's fun, I bet he's a very hot guy
It's wrong to fool around with your ex's siblings. You should just separate from her life entirely.
We will just forget each other, it's not going to affect us in the future.
I just don't think being connected to your ex in this way is healthy. I still think you should just leave them alone.