Not his dream girl

My partner and I kept having conflict over this girl from the past. I felt like he was still super attracted to her. He admitted she was his dream girl and if she hadn’t dropped him, he would choose her. I felt super insecure. He begged to talk because he felt like he had some epiphany. He proceeds to tell me his friends told him you have to lie in these scenarios…Even if I am not physically as attractive to him, I would think his love for me would make me his dream girl? My mom said I forced the issue by forcing these questions, but in our first talk, he also admitted to still thinking about her. Am I wrong for not wanting to be in second place? I am also disturbed this person has been so intimate with me, and feels like it would be a lie to say he prefers me?