Could my ex be the father?

Patient: I am not comfortable asking my obgyn about who the father may be because my fiance comes with me to my appointments…on December 26th I had unprotected sex with my ex and he ejaculated in me..and I had unprotected sex with my fiance later that night.. I started bleeding while having sex with my fiance. I bled for a few days or so and it was heavy like a normal period. I never had sex with my ex again and continued to have unprotected sex with my fiance. I had started my period again on February 7 and it ended on the 11th. I didn’t have a period in March. I found out I was pregnant in April and i had gone to my first ultrasound by the end of June. They had said my due date is December 8th. Is there any possible way that my ex could be the father? Please let me know because I have been very paranoid and anxious to hear from a doctor.