I agree with wfm. Just Say No!! And not just for the Cake Eating aspect, either - as if it isn't enough. I'm not a female, obviously, so I have no clue what the female sex drive while prego is like.
However, I do know what it's like to have to endure months at a time of no sex - it ain't no damn fun!! But, I'd rather do that than put my health at risk if I didn't know where my W has been - and more importantly, with whom... And it's easier for women to catch a disease than for men. Not to mention the act he pulled after the last time was about as classless as one can get, and had a negative emotional impact on you.
Again, not trying to be preachy - but, in the end, is it worth the risks right now?