Confused

Hi my name is nikita and I have a boyfriend that was diagnosed with ptsd when he was younger and just a couple of weeks ago diagnosed with borderline personality disorder. Every day he has flash backs of his ex sexually and non they broke up on August fourth and we got together August 20th. He had the flashbacks of her since we been together. Idk how I should feel. So far I feel like im just sloppy seconds. Please help what should I do and how should I really feel