My boyfriend cheated on me and I'm going to tell my coworker.
Is your coworker friends with the person with which your boyfriend cheated?
No, he is my coworker's enemy.
Are you close with your coworker? If not, telling them that your boyfriend cheated on you might make them uncomfortable.
I think my coworker will be very sad to hear the news.
While I'm sure your coworker would be sympathetic, sharing such private information in the workplace might make them uncomfortable and wouldn't be appropriate. Do you have a close friend who you can discuss this with? That would be a better solution and they'd be able to give you more support.