Ignore her. She'll either spill her guts or she won't. If she doesn't then all's well that ends well and if she doesI suspect your boyfrien would be upset that you considered it, and possibly angry too but I doubt very much he'll be splitting up with you over it so all's still well that ends well.
An ex of mine (we were still dating at the time) had a parent who committed suicide and over a deep and meaningful one night I told him that I'd been pretty close myself on two occasions. His response was that if I ever dared to attempt it he'd 'break me,' now admittedly this comment doesn't make an awful lot of sense but all it means is that he cares too much for me for me to do that as he'd miss me way too much. He's sad I considered it but he's glad he knows because now if I'm ever very low (which could still happen), he sort of keeps an eye on me. Not annoyingly so, but he just makes sure I know that the world as far as he's concerned is a better place with me in it. I expect that despite any sadness or anger, your boyfriend would/will feel much the same.