wanna find out who's my babys father without paternity test

Im unsure of who my baby fathers is. I had a one night stand with my ex. And my current bf doesnt know. If I am calculating correctly I believe my bf is the father. I believe i just finished my menstrual on nov 20th. My ex and I had intercourse the nov 23rd & 24th. He did say he ejaculated inside of me. We havnt had intercourse since. My current bf and I had sex around the same time nov 27th to Dec 1st. this was all after I had my period for the month of nov. I realized I can possibly be pregnant when I didnt get my menstrual in December. I took a test. And it came out positive. I did a online calculation and it says conception was dec 4th? And my due date is August 21-27th.Although my doctor gave me similar answers. I wanna find out who is possibly my babys father without a paternity test. Any help is appreciated, I am trying everything I can to try to figure this out, im so stressed over this. I would be devasted if the ex if the father.