It's precisely the fear of post-act blackmail which has deterred me from even contemplating it. A similar fear reared its head with a random civvy encounter, the house was empty but I wouldn't have been keen on her knowing where I live and the fact I was attached.
This does remind me of when I did have to stay living with an ex (flat deposit etc.) And started seeing someone else. Only did it with her in the bed shared with ex the once as I couldn't concentrate doing her doggy as she passed comment on all my ex's stuff around us.