The sister in law Anna has been in something before. Gormangast in 2000.
I liked the last episode, just watched it now. I have a theory that Rita was still sleeping with this man who is supposedly Lucy's father becuase she wanted all of her kiRAB to be fathered by the same man, for some odd reason, to do with her being adopted. She then used protection with her husband, or boyfriend or what ever he was to her.
I'm probably wrong.
The most probable explanation is that the guy just thinks this, becuase he feels betrayed by Rita for not telling him that he had been in contact with Lucy's father all of these years.