Love in the workplace

Nice girl in the car tonight with a bit of a dilemma;
Her work colleague has sworn his undying love for her.
This is understandable on two counts;
Firstly, she was a lovely girl.
Secondly, working in close proximity to someone you build up a relationship easily, having lots in common (work and work colleagues).
In this instance he's mistaken friendship and intimate chats about both their lives as more than she'd imagined.
Thing is, this guys Married and about 12 years her senior (early 30s V mid 40s) although she said she'd be going out with him if he wasn't married.
I can sense big trouble brewing!