How do I get over his ex girlfriend? 10 POINTS!!!!....?

Sometimes I get curious about my boyfriend's ex and their relationship. They dated for 3 years, and we are going on 6 months. Things are amazing right now. But yesterday we were driving and I asked him if he ever got oral while driving and he said,"Ya, but only for 5 seconds" We were joking around about it and I didn't care, but after a while of thinking about it, I just got jealous and regretted that question. I wonder if she was better at sex, or if she was more spontaneous. How can I get over this?? They had sex everywhere. In Parks, at the beach. Everywhere we go I wonder if he thinks about her and if he is bringing me to the same spot with her. What do I do?