'We can't, Andrew'

they had the affair after Lena was born. I think he's Jay's father.

It's pretty obvious by now it's Catherine.

Julia was already in an 'incestuous' relationship with Baz, and Pope made it clear last episode he only saw her as a sister just as Baz should've. Add to that, Baz said Pope was always in love with Catherine since there were kids, so there's no reason for him to have an incestuous relationship with his sister. Yes, it was mentioned several times they slept in the same bed for a while, but so did a lot of twins siblings in their childhood, it shouldn't come as a surprise that as twins they were closer than most siblings would be.

I think it implies that it's Smurf or Julia... Perhaps Pope did have a thing with his twin , Julia but Baz actually got to be with her because they weren't blood ... & he also got Cath... But again I definitely think it was left open that it could've been about Smurf

I think it was Julia. I think Pope is J's dad. I don't think it's a coincidence the characters dress similar and sometimes they are filmed in the same way with the same lighting.

The Cath/Pope hook up seems to have happened because Cath was pissed at Baz (my guess is that she found out he was cheating). So I don't think Cath was saying "we can't Andrew" because it seems she seek out Pope to get back at Baz.

I feel there was a love square (Pope/Julia/Baz/Cath) when they were all teenagers but Cath had no idea about Pope/Julia. I think Baz knew about Pope/Julia and that's why he rejects J all the time. He suspects Pope might be his father.