Because he loves Seka and this is all he has left of her.
Because he's loved this kid since it was inside her and being out side of her doesn't change his heart's momentum.
Remember My name is earl?
"I can't blame my son because his mother is a whore"
(that can't be the line from the pilot when Earl found a black child climbing out of his wife... but he stayed!)
Meanwhile the Doctor was lying his ass off as he was directing Suder to go out and kill people and sabotage shit while he was hiding kazon bodies in his stasis draws.
His lie mode was totally on.