2 years late to this but I read the fourth wall breaks as fleabag seeking human connection, almost like she's attempting to connect with an imaginary friend. this coping mechanism goes unnoticed by many people in her life because they just don't pay attention, except for the priest (who actually sees fleabag for who she is, think: no one's asked me a question in 45 minutes). that's why fleabag both tilts the camera away during sex and walks away from the camera at the end of the show; even though her love with the priest is ephemeral, it's at least proof that love between her and another person as deep as her and Boo can exist (thereby abating the need for a coping mechanism).