Did you skip the tutorial? The hearts drain stamina if you're inside when they pop. The strategy is to time things to fill the pleasure bar before running out of stamina.
I had the same issue, but I think I saw a dialogue box pop up and then disappear before displaying any text. As I learned myself, tweens (the things that let things fade in and out or transition from one position from another smoothly without having to make an animation track) can be a real bitch to use just how the engine wants you to so it won't cause that kind of problem.