Why don't you suggest fun distractions? If she starts talking about him, tell her you want to help her forget about him and move on. Instead of indulging her, just cut the reminiscences off, tell her she needs to look forwards and not backwards, and if she insists on talking about him, set a time limit, say okay, I'll listen for the next five minutes, or until I've finished this drink, and then we're going to change the subject and forget about him for the rest of the night. Suggest going to see a film, or going to a gig or the theatre, to give her something to look forward to and take her mind of it all.
And then see how it goes from there.