paternity

Please no judgement😩so, me and my ex partner split up a while back. I had intercourse with a guy on the 21st of June just the once. Then me and my ex partner ended up getting back together on the 21st of July and were sleeping together daily since that day. I then had a positive pregnant test on the 5th of August. My first ultrasound on the 13th of September dated me at 9weeks and 2 days pregnant. Then my most recent ultrasound dated me to be exactly 15 weeks on the 19th of October with a due date of 12/04/2025. I don’t remember any period dates due to having PCOS, I have a prenatal paternity test booked to find out for definite but just want help working out who is most likely the father? can it still possibly be both even with over 4 weeks difference? Any advice appreciated