
What do you mean. He had a physical relationship with the beta. Just imagine a person who you have relationship with( and you slept wjth him) and that person cheats on you by sleeping with your dad or mom. And later on he she becomes your stepdad/mom. Im sorry thats incest to me.
Thats kinda disgusting. And plus having a brother.
If it isnt incest to me it is still taboo.

The thing is, they were together before they were a family, but it's weird that your ex suddenly becomes your stepfather. I think it's a bit of a grey area, idk if it's incest or not but it is definitely weird, there's no denying it. Also, I would rather not imagine my family members and exes having sex thank you for the horror image, I'm gonna have nightmares with that now D:
The spoilers from the comments tell me that the relationships between them is really messed up. They should add an incest tag.