DIVULGING HURTFUL INFO

[Love Child]

If you know about something being said or done to someone you like and whose feelings you care about, do you tell them even when it will serve no purpose to do so?

I know what I would do but I'm curious how others would handle that.

There is a co-worker who works in a different department than I do, and she likes a guy I work with. I am pretty sure he does not prefer females, but is not open about it. In fact he hides it pretty well.
Do I tell her?