Did you know I'm in love with an older married coworker even though I'm engaged?
That sounds like an intense situation. Can you share with me what brought this on?
He wasn't interested in his wife anymore.
You can't help who you're attracted to. It's not good to fall for coworkers it can lead to tension at work and might not be ethical.
We are not dating. I love him but I won't break up with my fiance
I think you're making the correct decision to not act on your feelings. My advice would be to keep the relationship with your coworker strictly professional and what you feel will eventually pass.