I’d be more worried that the two of you hook up, and then it ends badly.If you do have the talk, talk in detail: Don’t just tell him you’re falling for him, make it clear that you’re interested in something serious and that you’d be hurt if he wasn’t looking for something real as well. My only other worry here is that you say she’s “a friend” of your fiancé.
There's always been chemistry between us, but now that I'm at a new company we've been meeting each other regularly as friends and the chemistry just grows each time.
I think the only reason we're holding back is because of the age difference.
It’s a good thing to have friendly contacts in your industry—and a romance that fizzles could burn more than the friendship.
It could burn a valuable professional relationship with a senior colleague, or potentially tarnish your reputation if it turns out you’re just his next lady.
She just needs to stop because it’s not cool; it’s lame and disrespectful to you.