Broadway Flash said: "Not a prude, just don’t think it’s pleasant to watch on stage. Aspects of Love they each had sex with each other (including with family members) but it was so exquisite andelegant not trashy and awkward"
I apologize for drifting off topic, but did the recent London production imply that Alex and Jenny had a sexual relationship? In the versions I've seen, Alex does lie down fully clothed with Jenny to comfort her, precipitating George's death, but there is no indication that they have sex.
For the record, if they did, the fact that Jenny is 15 is a bigger problem for me than the fact that she's his cousin. The latter fact is icky but hardly unprecedented (see: Victoria and Albert).