Why would they take this angle?

Debs therapist telling her her history with tumultuous relationships is because she might be in love with dexter and not the fact harry neglected her for years and she grew up without a mother figure for most of her life AND that she’s literally in a high stress job every day is insane. I had a friend spoil it for me that the show would take this route but seeing that its the therapist basically planting this bizarre train of thought in debs mind is just crazy and makes no sense at all. She’s known dexter as her brother since she was born. All her life. It doesn’t even make sense